/* ==========================================================================
   tokens.css — monochrome design tokens.
   Strict black-and-white system: every surface, border, label, state and
   syntax color is a pure neutral gray (R=G=B) — zero hue anywhere.
   Hierarchy comes from lightness, font weight and spacing, never color.
   Static ramp on :root; dark overrides on html[data-ds-dark-theme].
   ========================================================================== */

:root {
  /* -- neutral ramp (pure grayscale, R=G=B, no blue tint) ---------------- */
  --dsw-neutral-00: rgb(255, 255, 255);
  --dsw-neutral-1000: rgb(0, 0, 0);
  --dsw-neutral-50: rgb(250, 250, 250);

  --dsw-bluish-00: rgb(255, 255, 255);
  --dsw-bluish-50: rgb(250, 250, 250);
  --dsw-bluish-60: rgb(247, 247, 247);
  --dsw-bluish-75: rgb(242, 242, 242);
  --dsw-bluish-100: rgb(237, 237, 237);
  --dsw-bluish-150: rgb(232, 232, 232);
  --dsw-bluish-200: rgb(226, 226, 226);
  --dsw-bluish-300: rgb(212, 212, 212);
  --dsw-bluish-400: rgb(179, 179, 179);
  --dsw-bluish-500: rgb(153, 153, 153);
  --dsw-bluish-600: rgb(128, 128, 128);
  --dsw-bluish-700: rgb(102, 102, 102);
  --dsw-bluish-750: rgb(82, 82, 82);
  --dsw-bluish-800: rgb(64, 64, 64);
  --dsw-bluish-850: rgb(46, 46, 46);
  --dsw-bluish-875: rgb(36, 36, 36);
  --dsw-bluish-900: rgb(26, 26, 26);
  --dsw-bluish-950: rgb(16, 16, 16);
  --dsw-bluish-1000: rgb(10, 10, 10);

  /* accent ramp stays neutral: light accent is near-black, dark is white */
  --dsw-deepseek-50: rgb(242, 242, 242);
  --dsw-deepseek-100: rgb(232, 232, 232);
  --dsw-deepseek-200: rgb(212, 212, 212);
  --dsw-deepseek-300: rgb(179, 179, 179);
  --dsw-deepseek-400: rgb(46, 46, 46);
  --dsw-deepseek-450: rgb(31, 31, 31);
  --dsw-deepseek-500: rgb(10, 10, 10);
  --dsw-deepseek-800: rgb(51, 51, 51);
  --dsw-deepseek-900: rgb(17, 17, 17);

  /* status ramps collapse to grayscale as well */
  --dsw-green-100: rgb(242, 242, 242);
  --dsw-green-400: rgb(26, 26, 26);
  --dsw-green-500: rgb(10, 10, 10);
  --dsw-green-900: rgb(36, 36, 36);
  --dsw-red-100: rgb(237, 237, 237);
  --dsw-red-400: rgb(153, 153, 153);
  --dsw-red-600: rgb(128, 128, 128);
  --dsw-red-900: rgb(46, 46, 46);
  --dsw-amber-100: rgb(247, 247, 247);
  --dsw-amber-400: rgb(179, 179, 179);
  --dsw-amber-500: rgb(102, 102, 102);
  --dsw-amber-600: rgb(82, 82, 82);
  --dsw-amber-900: rgb(31, 31, 31);
  --dsw-blue-800: rgb(26, 26, 26);
  --dsw-blue-900: rgb(10, 10, 10);

  /* -- semantic aliases (light) ------------------------------------------- */
  --ds-bg-base: var(--dsw-bluish-00);
  --ds-bg-layer-1: var(--dsw-bluish-00);
  --ds-bg-layer-2: var(--dsw-bluish-00);
  --ds-bg-layer-3: var(--dsw-bluish-00);
  --ds-bg-sidebar: var(--dsw-bluish-50);
  --ds-bg-hover: rgba(0, 0, 0, 0.05);
  --ds-bg-hover-strong: rgba(0, 0, 0, 0.09);
  --ds-bg-active: rgba(0, 0, 0, 0.13);
  --ds-bg-soft: var(--dsw-bluish-50);
  --ds-bg-tip: var(--dsw-bluish-60);
  --ds-bg-mask: rgba(0, 0, 0, 0.24);

  --ds-label-primary: var(--dsw-bluish-1000);
  --ds-label-secondary: var(--dsw-bluish-700);
  --ds-label-tertiary: var(--dsw-bluish-600);
  --ds-label-caption: var(--dsw-bluish-500);
  --ds-label-on-brand: var(--dsw-bluish-00);

  --ds-border-l1: rgba(0, 0, 0, 0.06);
  --ds-border-l2: rgba(0, 0, 0, 0.1);
  --ds-border-l3: rgba(0, 0, 0, 0.14);
  --ds-border-l4: rgba(0, 0, 0, 0.18);

  --ds-accent: var(--dsw-deepseek-500);        /* near-black */
  --ds-accent-hover: var(--dsw-deepseek-400);
  --ds-accent-soft: var(--dsw-deepseek-50);
  --ds-accent-border: var(--dsw-deepseek-100);
  --ds-accent-ink: var(--dsw-blue-900);

  --ds-mark-code-block: var(--dsw-bluish-50);
  --ds-mark-code-banner: var(--dsw-bluish-50);
  --ds-mark-inline-code: var(--dsw-bluish-100);
  --ds-mark-tag: var(--dsw-bluish-75);
  --ds-mark-citation: var(--dsw-bluish-100);

  --ds-success: var(--dsw-bluish-1000);         /* strongest = correct */
  --ds-success-soft: var(--dsw-bluish-75);
  --ds-warn: var(--dsw-bluish-750);
  --ds-warn-ink: var(--dsw-bluish-800);
  --ds-warn-soft: var(--dsw-bluish-60);
  --ds-error: var(--dsw-bluish-700);            /* mid gray = wrong */
  --ds-error-soft: var(--dsw-bluish-100);

  --ds-tooltip-bg: var(--dsw-bluish-850);
  --ds-tooltip-ink: var(--dsw-bluish-00);
  --ds-scrollbar: var(--dsw-bluish-200);
  --ds-scrollbar-hover: var(--dsw-bluish-300);

  --ds-shadow-1: 0 1px 2px rgba(0, 0, 0, 0.04), 0 1px 2px rgba(0, 0, 0, 0.06);
  --ds-shadow-2: 0 2px 6px rgba(0, 0, 0, 0.06), 0 8px 24px rgba(0, 0, 0, 0.08);

  /* -- syntax tokens (light): grayscale + weight carries the meaning ----- */
  --syn-foreground: rgb(26, 26, 26);
  --syn-background: var(--ds-mark-code-block);
  --syn-constant: rgb(10, 10, 10);
  --syn-string: rgb(85, 85, 85);
  --syn-comment: rgb(138, 138, 138);
  --syn-keyword: rgb(10, 10, 10);
  --syn-parameter: rgb(85, 85, 85);
  --syn-function: rgb(31, 31, 31);
  --syn-punctuation: rgb(110, 110, 110);
  --syn-number: rgb(68, 68, 68);

  /* -- typography ---------------------------------------------------------- */
  --ds-font: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'PingFang SC',
    'Hiragino Sans GB', 'Microsoft YaHei', 'Helvetica Neue', Helvetica, Arial,
    sans-serif;
  --ds-font-code: 'SF Mono', 'JetBrains Mono', 'Fira Code', Consolas,
    'Liberation Mono', Menlo, Courier, 'PingFang SC', 'Microsoft YaHei';

  /* -- motion -------------------------------------------------------------- */
  --ds-ease: cubic-bezier(0.4, 0, 0.2, 1);
  --ds-dur-fast: 0.1s;
  --ds-dur: 0.2s;
  --ds-dur-slow: 0.3s;

  /* -- layout metrics ------------------------------------------------------- */
  --ds-navbar-h: 56px;
  --ds-sidebar-w: 288px;
  --ds-toc-w: 232px;
  /* Reading column. Usage sites cap it with min(var(--ds-content-w), 100%)
   * so narrow viewports shrink it instead of overflowing. */
  --ds-content-w: 880px;
  --ds-radius-sm: 6px;
  --ds-radius: 8px;
  --ds-radius-lg: 12px;
}

/* ==========================================================================
   Dark theme — true black canvas, white ink, fully inverted controls.
   ========================================================================== */
html[data-ds-dark-theme] {
  color-scheme: dark;

  --ds-bg-base: rgb(0, 0, 0);
  --ds-bg-layer-1: rgb(13, 13, 13);
  --ds-bg-layer-2: rgb(21, 21, 21);
  --ds-bg-layer-3: rgb(30, 30, 30);
  --ds-bg-sidebar: rgb(10, 10, 10);
  --ds-bg-hover: rgba(255, 255, 255, 0.08);
  --ds-bg-hover-strong: rgba(255, 255, 255, 0.12);
  --ds-bg-active: rgba(255, 255, 255, 0.16);
  --ds-bg-soft: rgb(16, 16, 16);
  --ds-bg-tip: rgb(21, 21, 21);
  --ds-bg-mask: rgba(0, 0, 0, 0.6);

  --ds-label-primary: rgb(255, 255, 255);
  --ds-label-secondary: rgb(199, 199, 199);
  --ds-label-tertiary: rgb(163, 163, 163);
  --ds-label-caption: rgb(125, 125, 125);
  --ds-label-on-brand: rgb(0, 0, 0);

  --ds-border-l1: rgba(255, 255, 255, 0.08);
  --ds-border-l2: rgba(255, 255, 255, 0.14);
  --ds-border-l3: rgba(255, 255, 255, 0.18);
  --ds-border-l4: rgba(255, 255, 255, 0.22);

  --ds-accent: rgb(255, 255, 255);
  --ds-accent-hover: rgb(214, 214, 214);
  --ds-accent-soft: rgba(255, 255, 255, 0.08);
  --ds-accent-border: rgba(255, 255, 255, 0.2);
  --ds-accent-ink: rgb(242, 242, 242);

  --ds-mark-code-block: rgb(14, 14, 14);
  --ds-mark-code-banner: rgb(21, 21, 21);
  --ds-mark-inline-code: rgb(28, 28, 28);
  --ds-mark-tag: rgb(28, 28, 28);
  --ds-mark-citation: rgb(30, 30, 30);

  --ds-success: rgb(255, 255, 255);
  --ds-success-soft: rgba(255, 255, 255, 0.1);
  --ds-warn: rgb(212, 212, 212);
  --ds-warn-ink: rgb(226, 226, 226);
  --ds-warn-soft: rgb(22, 22, 22);
  --ds-error: rgb(153, 153, 153);
  --ds-error-soft: rgba(255, 255, 255, 0.06);

  --ds-tooltip-bg: rgb(82, 82, 82);
  --ds-tooltip-ink: rgb(250, 250, 250);
  --ds-scrollbar: rgb(64, 64, 64);
  --ds-scrollbar-hover: rgb(102, 102, 102);

  --ds-shadow-1: 0 1px 2px rgba(0, 0, 0, 0.4);
  --ds-shadow-2: 0 2px 6px rgba(0, 0, 0, 0.4), 0 8px 24px rgba(0, 0, 0, 0.5);

  /* -- syntax tokens (dark): grayscale + weight --------------------------- */
  --syn-foreground: rgb(242, 242, 242);
  --syn-background: var(--ds-mark-code-block);
  --syn-constant: rgb(245, 245, 245);
  --syn-string: rgb(181, 181, 181);
  --syn-comment: rgb(128, 128, 128);
  --syn-keyword: rgb(255, 255, 255);
  --syn-parameter: rgb(181, 181, 181);
  --syn-function: rgb(232, 232, 232);
  --syn-punctuation: rgb(154, 154, 154);
  --syn-number: rgb(207, 207, 207);
}

/* ---------------------------------------------------------------------- */
/* Lesson-figure theme bridge. The vendored upstream figure runtime styles */
/* itself through these variable names; map them onto the monochrome       */
/* tokens so every interactive figure follows the theme, light or dark.    */
:root {
  --bg: var(--ds-bg-base);
  --bg-surface: var(--ds-bg-soft);
  --ink: var(--ds-label-primary);
  --ink-soft: var(--ds-label-secondary);
  --ink-mute: var(--ds-label-tertiary);
  --rule-soft: var(--ds-border-l2);
  --blueprint: var(--ds-accent);
  --blueprint-tint: var(--ds-accent-soft);
  --blueprint-tint-strong: rgba(0, 0, 0, 0.14);
  --code-bg: var(--ds-mark-code-block);
  --warn: var(--ds-warn);
  --danger: var(--ds-error);
  --font-body: var(--ds-font);
  --font-display: var(--ds-font);
  --font-mono: var(--ds-font-code);
  --ease-out: cubic-bezier(0.23, 1, 0.32, 1);
  --ease-in-out: cubic-bezier(0.77, 0, 0.175, 1);
  --motion-press: 160ms;
  --motion-feedback: 180ms;
  --motion-drawer: 250ms;
}

html[data-ds-dark-theme] {
  --blueprint-tint-strong: rgba(255, 255, 255, 0.18);
}

/* ==========================================================================
   base.css — reset, typography scale, focus, selection, scrollbars.
   ========================================================================== */

*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--ds-navbar-h) + 16px);
}

body {
  margin: 0;
  font-family: var(--ds-font);
  font-size: 16px;
  line-height: 1.75;
  color: var(--ds-label-primary);
  background: var(--ds-bg-base);
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  transition: background-color var(--ds-dur) var(--ds-ease),
    color var(--ds-dur) var(--ds-ease);
}

/* zh body copy breathes slightly more */
html[lang='zh'] body {
  line-height: 1.85;
}

img,
svg,
video {
  max-width: 100%;
  height: auto;
}

button {
  font: inherit;
  color: inherit;
  background: none;
  border: 0;
  padding: 0;
  cursor: pointer;
  touch-action: manipulation;
}

a {
  color: var(--ds-accent);
  text-decoration: none;
  transition: color var(--ds-dur-fast) var(--ds-ease);
}

a:hover {
  color: var(--ds-accent-hover);
  text-decoration: underline;
  text-underline-offset: 3px;
}

code,
kbd,
pre,
samp {
  font-family: var(--ds-font-code);
}

:focus-visible {
  outline: 2px solid var(--ds-accent);
  outline-offset: 2px;
  border-radius: 2px;
}

::selection {
  background: var(--dsw-bluish-1000);
  color: var(--dsw-bluish-00);
}

html[data-ds-dark-theme] ::selection {
  background: rgb(255, 255, 255);
  color: rgb(0, 0, 0);
}

/* Slim DeepSeek-style scrollbars */
* {
  scrollbar-width: thin;
  scrollbar-color: var(--ds-scrollbar) transparent;
}

*::-webkit-scrollbar {
  width: 8px;
  height: 8px;
}

*::-webkit-scrollbar-thumb {
  background: var(--ds-scrollbar);
  border-radius: 4px;
}

*::-webkit-scrollbar-thumb:hover {
  background: var(--ds-scrollbar-hover);
}

*::-webkit-scrollbar-track {
  background: transparent;
}

/* Screen-reader-only utility */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0 0 0 0);
  white-space: nowrap;
  border: 0;
}

.skip-link {
  position: fixed;
  top: -48px;
  left: 16px;
  z-index: 200;
  padding: 8px 16px;
  background: var(--ds-accent);
  color: var(--ds-label-on-brand);
  border-radius: var(--ds-radius-sm);
  transition: top var(--ds-dur) var(--ds-ease);
}

.skip-link:focus-visible {
  top: 8px;
  color: var(--ds-label-on-brand);
  text-decoration: none;
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

/* ==========================================================================
   layout.css — navbar, shell grid, sidebar, TOC, drawer, footer, pager.
   ========================================================================== */

/* -- navbar ---------------------------------------------------------------- */
.navbar {
  position: fixed;
  inset: 0 0 auto 0;
  z-index: 100;
  height: var(--ds-navbar-h);
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 0 16px;
  background: var(--ds-bg-layer-1);
  border-bottom: 1px solid var(--ds-border-l1);
  transition: background-color var(--ds-dur) var(--ds-ease),
    border-color var(--ds-dur) var(--ds-ease);
}

.navbar-brand {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-inline-end: 8px;
  color: var(--ds-label-primary);
  font-weight: 650;
  font-size: 15px;
  letter-spacing: -0.01em;
  white-space: nowrap;
}

.navbar-brand:hover {
  color: var(--ds-label-primary);
  text-decoration: none;
}

.brand-mark {
  display: grid;
  place-items: center;
  width: 28px;
  height: 28px;
  border-radius: 8px;
  background: var(--dsw-bluish-1000);
  color: var(--dsw-bluish-00);
  flex: none;
}

html[data-ds-dark-theme] .brand-mark {
  background: var(--dsw-bluish-50);
  color: var(--dsw-bluish-1000);
}

.brand-mark svg {
  width: 20px;
  height: 20px;
}

.navbar-spacer {
  flex: 1;
}

.navbar-link {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  height: 36px;
  padding: 0 10px;
  border-radius: var(--ds-radius-sm);
  color: var(--ds-label-secondary);
  font-size: 14px;
  white-space: nowrap;
}

.navbar-link:hover {
  background: var(--ds-bg-hover);
  color: var(--ds-label-primary);
  text-decoration: none;
}

/* Search trigger — looks like an input, opens the modal */
.navbar-search {
  display: flex;
  align-items: center;
  gap: 8px;
  width: 200px;
  height: 36px;
  padding: 0 8px 0 12px;
  border: 1px solid var(--ds-border-l2);
  border-radius: var(--ds-radius);
  color: var(--ds-label-tertiary);
  font-size: 13.5px;
  background: var(--ds-bg-base);
  transition: border-color var(--ds-dur-fast) var(--ds-ease),
    background-color var(--ds-dur-fast) var(--ds-ease);
}

.navbar-search:hover {
  border-color: var(--ds-border-l3);
  background: var(--ds-bg-hover);
  color: var(--ds-label-secondary);
}

.navbar-search kbd {
  margin-inline-start: auto;
  padding: 1px 6px;
  border: 1px solid var(--ds-border-l2);
  border-radius: 4px;
  font-size: 11px;
  line-height: 1.6;
  color: var(--ds-label-tertiary);
}

.icon-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  border-radius: var(--ds-radius-sm);
  color: var(--ds-label-secondary);
  transition: background-color var(--ds-dur-fast) var(--ds-ease),
    color var(--ds-dur-fast) var(--ds-ease);
}

.icon-btn:hover {
  background: var(--ds-bg-hover);
  color: var(--ds-label-primary);
}

.icon-btn svg {
  width: 18px;
  height: 18px;
}

/* Language switch — two-segment control */
.lang-switch {
  display: inline-flex;
  align-items: center;
  padding: 2px;
  gap: 2px;
  border: 1px solid var(--ds-border-l2);
  border-radius: var(--ds-radius-sm);
}

.lang-switch a {
  display: inline-flex;
  align-items: center;
  height: 26px;
  padding: 0 10px;
  border-radius: 4px;
  font-size: 12.5px;
  font-weight: 500;
  color: var(--ds-label-tertiary);
}

.lang-switch a:hover {
  color: var(--ds-label-primary);
  text-decoration: none;
}

.lang-switch a[aria-current='true'] {
  background: var(--ds-bg-active);
  color: var(--ds-label-primary);
}

.navbar .menu-btn {
  display: none;
}

/* -- shell grid ------------------------------------------------------------ */
.shell {
  display: grid;
  grid-template-columns: var(--ds-sidebar-w) minmax(0, 1fr) var(--ds-toc-w);
  padding-top: var(--ds-navbar-h);
  min-height: 100vh;
}

.main {
  padding: 32px 48px 64px;
  min-width: 0;
}

.content {
  max-width: min(var(--ds-content-w), 100%);
  margin: 0 auto;
}

/* -- sidebar ---------------------------------------------------------------- */
.sidebar {
  position: sticky;
  top: var(--ds-navbar-h);
  height: calc(100vh - var(--ds-navbar-h));
  overflow-y: auto;
  overscroll-behavior: contain;
  background: var(--ds-bg-sidebar);
  border-inline-end: 1px solid var(--ds-border-l1);
  padding: 16px 12px 32px;
  transition: background-color var(--ds-dur) var(--ds-ease);
}

.sidebar-scrim {
  display: none;
}

.nav-group {
  border-radius: var(--ds-radius);
}

.nav-group + .nav-group {
  margin-top: 2px;
}

.nav-group-head {
  display: flex;
  align-items: center;
  gap: 8px;
  width: 100%;
  padding: 7px 10px;
  border-radius: var(--ds-radius-sm);
  color: var(--ds-label-secondary);
  font-size: 14.5px;
  font-weight: 600;
  text-align: start;
  transition: background-color var(--ds-dur-fast) var(--ds-ease),
    color var(--ds-dur-fast) var(--ds-ease);
}

.nav-group-head:hover {
  background: var(--ds-bg-hover);
  color: var(--ds-label-primary);
}

.nav-phase-num {
  flex: none;
  display: inline-grid;
  place-items: center;
  min-width: 26px;
  height: 20px;
  padding: 0 6px;
  border-radius: 5px;
  background: var(--ds-mark-tag);
  color: var(--ds-label-tertiary);
  font-family: var(--ds-font-code);
  font-size: 11.5px;
  font-weight: 600;
}

.nav-group.current .nav-phase-num {
  background: var(--dsw-bluish-1000);
  color: var(--dsw-bluish-00);
}

html[data-ds-dark-theme] .nav-group.current .nav-phase-num {
  background: var(--dsw-bluish-50);
  color: var(--dsw-bluish-1000);
}

.nav-group-title {
  flex: 1;
  min-width: 0;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.nav-group-count {
  flex: none;
  font-size: 11.5px;
  color: var(--ds-label-caption);
  font-variant-numeric: tabular-nums;
}

.nav-chevron {
  flex: none;
  width: 14px;
  height: 14px;
  color: var(--ds-label-caption);
  transition: transform var(--ds-dur) var(--ds-ease);
}

.nav-group.open .nav-chevron {
  transform: rotate(90deg);
}

.nav-lessons {
  display: none;
  list-style: none;
  margin: 2px 0 6px;
  padding: 0 0 0 14px;
}

.nav-group.open > .nav-lessons {
  display: block;
}

.nav-lessons li {
  margin: 1px 0;
}

.nav-lessons a {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 5px 10px;
  border-radius: var(--ds-radius-sm);
  color: var(--ds-label-tertiary);
  font-size: 13.5px;
  line-height: 1.5;
  transition: background-color var(--ds-dur-fast) var(--ds-ease),
    color var(--ds-dur-fast) var(--ds-ease);
}

.nav-lessons a:hover {
  background: var(--ds-bg-hover);
  color: var(--ds-label-primary);
  text-decoration: none;
}

.nav-lessons a[aria-current='page'] {
  background: var(--ds-bg-hover);
  color: var(--ds-label-primary);
  font-weight: 600;
}

.nav-lessons .lesson-num {
  flex: none;
  font-family: var(--ds-font-code);
  font-size: 11.5px;
  color: var(--ds-label-caption);
  font-variant-numeric: tabular-nums;
}

.nav-lessons a[aria-current='page'] .lesson-num {
  color: var(--ds-label-primary);
}

.nav-loading {
  padding: 8px 10px;
  font-size: 12px;
  color: var(--ds-label-caption);
}

/* -- TOC --------------------------------------------------------------------- */
.toc {
  position: sticky;
  top: var(--ds-navbar-h);
  height: calc(100vh - var(--ds-navbar-h));
  overflow-y: auto;
  padding: 40px 20px 32px 8px;
  font-size: 13px;
}

.toc-title {
  margin: 0 0 10px;
  font-size: 11px;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--ds-label-caption);
}

.toc-list {
  list-style: none;
  margin: 0;
  padding: 0;
  border-inline-start: 1px solid var(--ds-border-l1);
}

.toc-list a {
  display: block;
  padding: 4px 0 4px 14px;
  color: var(--ds-label-tertiary);
  line-height: 1.5;
  border-inline-start: 2px solid transparent;
  margin-inline-start: -1.5px;
  transition: color var(--ds-dur-fast) var(--ds-ease),
    border-color var(--ds-dur-fast) var(--ds-ease);
}

.toc-list a:hover {
  color: var(--ds-label-primary);
  text-decoration: none;
}

.toc-list a.active {
  color: var(--ds-accent);
  border-inline-start-color: var(--ds-accent);
}

.toc-list .toc-h3 a {
  padding-inline-start: 26px;
  font-size: 12.5px;
}

/* -- lesson header ------------------------------------------------------------ */
.breadcrumb {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 6px;
  margin: 0 0 20px;
  font-size: 13px;
  color: var(--ds-label-tertiary);
}

.breadcrumb a {
  color: var(--ds-label-tertiary);
}

.breadcrumb a:hover {
  color: var(--ds-accent);
}

.breadcrumb .sep {
  color: var(--ds-label-caption);
}

.breadcrumb .here {
  color: var(--ds-label-secondary);
}

.lesson-title {
  margin: 0 0 8px;
  font-size: 34px;
  line-height: 1.25;
  font-weight: 700;
  letter-spacing: -0.02em;
}

html[lang='zh'] .lesson-title {
  letter-spacing: 0;
}

/* meta chips row (Type / Languages / Prerequisites / Time) */
.lesson-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin: 0 0 8px;
}

.meta-chip {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  height: 26px;
  padding: 0 10px;
  border: 1px solid var(--ds-border-l2);
  border-radius: 999px;
  font-size: 12.5px;
  color: var(--ds-label-secondary);
  background: var(--ds-bg-soft);
}

.meta-chip svg {
  width: 13px;
  height: 13px;
  color: var(--ds-label-tertiary);
}

.meta-chip b {
  font-weight: 600;
  color: var(--ds-label-primary);
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  height: 38px;
  padding: 0 16px;
  border-radius: var(--ds-radius);
  font-size: 14px;
  font-weight: 500;
  border: 1px solid var(--ds-border-l2);
  color: var(--ds-label-primary);
  background: var(--ds-bg-layer-1);
  transition: background-color var(--ds-dur-fast) var(--ds-ease),
    border-color var(--ds-dur-fast) var(--ds-ease),
    color var(--ds-dur-fast) var(--ds-ease);
}

.btn:hover {
  background: var(--ds-bg-hover);
  border-color: var(--ds-border-l3);
  text-decoration: none;
}

.btn svg {
  width: 15px;
  height: 15px;
}

.btn-primary {
  background: var(--dsw-bluish-1000);
  border-color: var(--dsw-bluish-1000);
  color: var(--dsw-bluish-00);
}

.btn-primary:hover {
  background: var(--dsw-bluish-750);
  border-color: var(--dsw-bluish-750);
  color: var(--dsw-bluish-00);
}

html[data-ds-dark-theme] .btn-primary {
  background: var(--dsw-bluish-50);
  border-color: var(--dsw-bluish-50);
  color: var(--dsw-bluish-1000);
}

html[data-ds-dark-theme] .btn-primary:hover {
  background: var(--dsw-bluish-100);
  border-color: var(--dsw-bluish-100);
  color: var(--dsw-bluish-1000);
}

/* -- pager --------------------------------------------------------------------- */
.pager {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  margin-top: 48px;
  padding-top: 24px;
  border-top: 1px solid var(--ds-border-l1);
}

.pager-card {
  display: flex;
  flex-direction: column;
  gap: 4px;
  padding: 14px 16px;
  border: 1px solid var(--ds-border-l2);
  border-radius: var(--ds-radius-lg);
  color: var(--ds-label-secondary);
  min-height: 44px;
  transition: border-color var(--ds-dur-fast) var(--ds-ease),
    background-color var(--ds-dur-fast) var(--ds-ease);
}

.pager-card:hover {
  border-color: var(--ds-border-l4);
  background: var(--ds-bg-hover);
  color: var(--ds-label-primary);
  text-decoration: none;
}

.pager-card.next {
  text-align: end;
  grid-column: 2;
}

.pager-card .pager-label {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 12px;
  color: var(--ds-label-caption);
}

.pager-card.next .pager-label {
  justify-content: flex-end;
}

.pager-card .pager-title {
  font-size: 14px;
  font-weight: 550;
  color: var(--ds-label-primary);
}

.pager-label svg {
  width: 13px;
  height: 13px;
}

.pager-empty {
  visibility: hidden;
}

/* -- footer ---------------------------------------------------------------------- */
.footer {
  max-width: min(var(--ds-content-w), 100%);
  margin: 0 auto;
  padding: 24px 0 8px;
  border-top: 1px solid var(--ds-border-l1);
  font-size: 13px;
  color: var(--ds-label-tertiary);
  text-align: center;
}

.footer a {
  color: var(--ds-label-secondary);
}

/* -- site motto (big quote above the footer; NOT the lesson hook, which
   uses .content .motto in content.css — don't reuse that class name) ------- */
.site-motto {
  max-width: min(var(--ds-content-w), 100%);
  margin: 56px auto 0;
  text-align: center;
}

.motto-text {
  margin: 0;
  font-size: 28px;
  font-weight: 700;
  line-height: 1.4;
  letter-spacing: -0.015em;
  color: var(--ds-accent);
}

.motto-by {
  margin: 10px 0 0;
  font-size: 13px;
  color: var(--ds-label-caption);
}

@media (max-width: 479px) {
  .motto-text {
    font-size: 21px;
  }
}

/* -- responsive ------------------------------------------------------------------- */
@media (max-width: 1279px) {
  .toc {
    display: none;
  }

  .shell {
    grid-template-columns: var(--ds-sidebar-w) minmax(0, 1fr);
  }
}

/* Mid-size viewports: keep the TOC visible and still give .content at least
   its former 780px by slimming the fixed columns instead — 240 + 184 + 2×32
   + 780 = 1268 fits a 1280px viewport. */
@media (min-width: 1280px) and (max-width: 1439px) {
  :root {
    --ds-sidebar-w: 240px;
    --ds-toc-w: 184px;
  }

  .main {
    padding-inline: 32px;
  }
}

@media (max-width: 959px) {
  .shell {
    grid-template-columns: minmax(0, 1fr);
  }

  .main {
    padding: 24px 20px 56px;
  }

  /* Sidebar becomes an off-canvas drawer */
  .sidebar {
    position: fixed;
    inset: var(--ds-navbar-h) auto 0 0;
    z-index: 90;
    width: min(320px, 84vw);
    transform: translateX(-102%);
    transition: transform var(--ds-dur) var(--ds-ease);
    border-inline-end: 1px solid var(--ds-border-l2);
  }

  .sidebar.open {
    transform: translateX(0);
  }

  .sidebar-scrim {
    display: block;
    position: fixed;
    inset: var(--ds-navbar-h) 0 0 0;
    z-index: 80;
    background: var(--ds-bg-mask);
    opacity: 0;
    pointer-events: none;
    transition: opacity var(--ds-dur) var(--ds-ease);
  }

  .sidebar-scrim.show {
    opacity: 1;
    pointer-events: auto;
  }

  .navbar .menu-btn {
    display: inline-flex;
  }

  .navbar-search {
    width: auto;
    flex: 1;
    max-width: 200px;
  }

  .navbar-search .search-text,
  .navbar-search kbd {
    display: none;
  }

  .lang-switch a span.lang-full {
    display: none;
  }

  .pager {
    grid-template-columns: 1fr;
  }

  .pager-card.next {
    grid-column: auto;
  }
}

@media (max-width: 479px) {
  .lesson-title {
    font-size: 27px;
  }

  .navbar-link.github-text {
    display: none;
  }
}

/* -- learning-map nav row (sits above phase 00) ----------------------------- */
a.nav-group-head {
  text-decoration: none;
}

.nav-special .nav-phase-num {
  background: var(--ds-accent-soft);
  color: var(--ds-accent-ink);
  min-width: 26px;
}

.nav-special .nav-phase-num svg {
  display: block;
}

.nav-special.current .nav-group-title {
  color: var(--ds-label-primary);
  font-weight: 600;
}

/* ==========================================================================
   content.css — markdown body typography: headings, code, math, mermaid,
   tables, quotes, lists, figures. Styles the exact markup the vendored
   lesson-markdown.js emits.
   ========================================================================== */

.content {
  font-size: 16px;
}

/* -- headings ---------------------------------------------------------------- */
.content h1 {
  margin: 8px 0 20px;
  font-size: 30px;
  line-height: 1.3;
  font-weight: 700;
  letter-spacing: -0.015em;
}

.content h2 {
  margin: 44px 0 14px;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--ds-border-l1);
  font-size: 23px;
  line-height: 1.35;
  font-weight: 650;
  letter-spacing: -0.01em;
}

.content h3 {
  margin: 30px 0 10px;
  font-size: 18px;
  line-height: 1.4;
  font-weight: 620;
}

.content h4 {
  margin: 26px 0 8px;
  font-size: 16.5px;
  line-height: 1.45;
  font-weight: 640;
}

.content h5 {
  margin: 22px 0 6px;
  font-size: 16px;
  line-height: 1.5;
  font-weight: 620;
}

.content h2 .h2-icon,
.content h1 svg {
  display: inline-flex;
  vertical-align: -3px;
  margin-inline-end: 6px;
  color: var(--ds-accent);
}

/* -- motto (lesson hook) + drop cap ------------------------------------------- */
.content .motto {
  margin: 4px 0 20px;
  padding: 2px 0 2px 16px;
  border-inline-start: 3px solid var(--ds-accent);
  font-size: 17.5px;
  line-height: 1.7;
  color: var(--ds-label-secondary);
}

.content .drop-cap::first-letter {
  float: inline-start;
  font-size: 2.7em;
  line-height: 0.85;
  padding-inline-end: 8px;
  padding-top: 4px;
  font-weight: 650;
  color: var(--ds-label-primary);
}

html[lang='zh'] .content .drop-cap::first-letter {
  float: none;
  font-size: inherit;
  line-height: inherit;
  padding: 0;
  font-weight: inherit;
}

/* -- paragraphs, lists, rules -------------------------------------------------- */
.content p {
  margin: 0 0 16px;
}

.content ul,
.content ol {
  margin: 0 0 16px;
  padding-inline-start: 26px;
}

.content li {
  margin: 6px 0;
}

.content li::marker {
  color: var(--ds-label-caption);
}

.content hr {
  margin: 36px 0;
  border: 0;
  border-top: 1px solid var(--ds-border-l1);
}

/* -- inline code ----------------------------------------------------------------- */
.content code {
  padding: 1.5px 6px;
  border-radius: 5px;
  background: var(--ds-mark-inline-code);
  font-size: 0.875em;
  color: var(--ds-label-primary);
}

/* -- code blocks ------------------------------------------------------------------- */
.content pre {
  position: relative;
  margin: 20px 0;
  padding: 34px 18px 16px;
  border: 1px solid var(--ds-border-l1);
  border-radius: var(--ds-radius-lg);
  background: var(--ds-mark-code-block);
  overflow-x: auto;
  font-size: 13.5px;
  line-height: 1.7;
  transition: background-color var(--ds-dur) var(--ds-ease),
    border-color var(--ds-dur) var(--ds-ease);
}

.content pre code {
  padding: 0;
  background: none;
  font-size: inherit;
  color: var(--syn-foreground);
}

.content pre .code-lang {
  position: absolute;
  top: 9px;
  inset-inline-end: 44px;
  font-family: var(--ds-font-code);
  font-size: 11px;
  letter-spacing: 0.04em;
  color: var(--ds-label-caption);
  text-transform: lowercase;
}

.content pre .code-copy {
  position: absolute;
  top: 6px;
  inset-inline-end: 8px;
  display: inline-flex;
  align-items: center;
  gap: 4px;
  height: 26px;
  padding: 0 8px;
  border-radius: var(--ds-radius-sm);
  font-size: 11.5px;
  color: var(--ds-label-tertiary);
  opacity: 0;
  transition: opacity var(--ds-dur) var(--ds-ease),
    background-color var(--ds-dur-fast) var(--ds-ease),
    color var(--ds-dur-fast) var(--ds-ease);
}

.content pre:hover .code-copy,
.content pre .code-copy:focus-visible {
  opacity: 1;
}

.content pre .code-copy:hover {
  background: var(--ds-bg-hover-strong);
  color: var(--ds-label-primary);
}

.content pre .code-copy.copied {
  color: var(--ds-success);
  opacity: 1;
}

/* syntax tokens (highlightSyntax output) — monochrome: grayscale + weight */
.syn-comment { color: var(--syn-comment); font-style: italic; }
.syn-string { color: var(--syn-string); }
.syn-keyword { color: var(--syn-keyword); font-weight: 700; }
.syn-number { color: var(--syn-number); }
.syn-constant { color: var(--syn-constant); font-weight: 600; }
.syn-function { color: var(--syn-function); font-weight: 600; }
.syn-punctuation { color: var(--syn-punctuation); }
.syn-parameter { color: var(--syn-parameter); }

/* -- math ---------------------------------------------------------------------------- */
.content .math-display {
  margin: 20px 0;
  padding: 18px 20px;
  border: 1px solid var(--ds-border-l1);
  border-radius: var(--ds-radius-lg);
  background: var(--ds-mark-code-block);
  overflow-x: auto;
  font-family: var(--ds-font-code);
  font-size: 14.5px;
  line-height: 1.9;
  color: var(--syn-foreground);
  white-space: pre;
}

.content .math-inline {
  font-family: var(--ds-font-code);
  font-size: 0.9em;
  color: var(--syn-foreground);
  background: var(--ds-mark-inline-code);
  padding: 1px 5px;
  border-radius: 4px;
}

/* KaTeX replaces node content once loaded */
.content .math-display .katex-display {
  margin: 0;
  padding: 4px 0;
}

.content .math-display .katex,
.content .math-inline .katex {
  font-size: 1.08em;
}

/* -- mermaid --------------------------------------------------------------------------- */
.content .mermaid-container {
  margin: 20px 0;
}

.content .mermaid-block {
  border: 1px solid var(--ds-border-l1);
  border-radius: var(--ds-radius-lg);
  background: var(--ds-mark-code-block);
  overflow: hidden;
}

.content .mermaid-block .mermaid-source {
  margin: 0;
  padding: 14px 18px;
  border: 0;
  background: transparent;
  font-size: 12.5px;
  line-height: 1.6;
  color: var(--ds-label-secondary);
}

.content .mermaid-block .mermaid-render {
  padding: 16px;
  display: none;
  overflow-x: auto;
}

.content .mermaid-block.rendered .mermaid-source {
  display: none;
}

.content .mermaid-block.rendered .mermaid-render {
  display: block;
}

.content .mermaid-render svg {
  max-width: 100%;
  height: auto;
  margin: 0 auto;
  display: block;
}

/* -- figure placeholder -------------------------------------------------------------------- */
.content .figure-placeholder {
  display: flex;
  align-items: center;
  gap: 14px;
  margin: 20px 0;
  padding: 16px 20px;
  border: 1px dashed var(--ds-border-l3);
  border-radius: var(--ds-radius-lg);
  background: var(--ds-bg-soft);
}

.content .figure-placeholder .figure-icon {
  flex: none;
  display: grid;
  place-items: center;
  width: 38px;
  height: 38px;
  border-radius: var(--ds-radius);
  background: var(--ds-accent-soft);
  color: var(--ds-accent);
}

.content .figure-placeholder figcaption {
  display: flex;
  flex-direction: column;
  gap: 2px;
  min-width: 0;
}

.content .figure-placeholder .figure-key {
  font-family: var(--ds-font-code);
  font-size: 13px;
  font-weight: 600;
  color: var(--ds-label-secondary);
  overflow-wrap: anywhere;
}

.content .figure-placeholder .figure-note {
  font-size: 12.5px;
  color: var(--ds-label-caption);
}

/* Mounted interactive figures: the runtime injects its own chrome (.lf),
 * the host just needs spacing; the fallback card inside sits flush. */
.content .lesson-figure {
  margin: 0;
}

.content .lesson-figure[data-lf-mounted] {
  margin: 28px 0;
}

.content .lesson-figure[data-lf-mounted] > .figure-placeholder {
  display: none;
}

.content .lesson-figure[data-figure-missing] > .figure-placeholder {
  margin: 20px 0;
}

/* -- images, tables, quotes -------------------------------------------------------------------- */
.content img {
  display: block;
  margin: 20px auto;
  border: 1px solid var(--ds-border-l1);
  border-radius: var(--ds-radius-lg);
  background: var(--dsw-bluish-00);
}

html[data-ds-dark-theme] .content img {
  background: var(--dsw-bluish-00);
}

.content .table-wrap {
  margin: 20px 0;
  overflow-x: auto;
  border: 1px solid var(--ds-border-l1);
  border-radius: var(--ds-radius-lg);
}

.content table {
  width: 100%;
  border-collapse: collapse;
  font-size: 14px;
  line-height: 1.6;
}

.content th {
  padding: 10px 14px;
  text-align: start;
  font-weight: 620;
  font-size: 13px;
  color: var(--ds-label-secondary);
  background: var(--ds-bg-soft);
  border-bottom: 1px solid var(--ds-border-l2);
  white-space: nowrap;
}

.content td {
  padding: 10px 14px;
  border-bottom: 1px solid var(--ds-border-l1);
  vertical-align: top;
}

.content tbody tr:last-child td {
  border-bottom: 0;
}

.content tbody tr {
  transition: background-color var(--ds-dur-fast) var(--ds-ease);
}

.content tbody tr:hover {
  background: var(--ds-bg-hover);
}

.content blockquote {
  margin: 20px 0;
  padding: 10px 18px;
  border-inline-start: 3px solid var(--ds-accent-border);
  border-radius: 0 var(--ds-radius) var(--ds-radius) 0;
  background: var(--ds-bg-soft);
  color: var(--ds-label-secondary);
}

.content blockquote p {
  margin: 0;
}

/* -- special cards -------------------------------------------------------------------------------- */
.content .lesson-meta-tag {
  display: inline-block;
  margin: 0 6px 6px 0;
  padding: 2px 10px;
  border: 1px solid var(--ds-border-l2);
  border-radius: 999px;
  background: var(--ds-mark-tag);
  font-size: 12.5px;
  color: var(--ds-label-secondary);
}

.content .learning-objectives {
  margin: 20px 0 24px;
  padding: 16px 20px;
  border: 1px solid var(--ds-accent-border);
  border-radius: var(--ds-radius-lg);
  background: var(--ds-accent-soft);
}

.content .learning-objectives-title {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-bottom: 8px;
  font-size: 13px;
  font-weight: 650;
  letter-spacing: 0.02em;
  color: var(--ds-accent-ink);
}

.content .learning-objectives-title .lo-icon {
  display: inline-flex;
  color: var(--ds-accent);
}

.content .learning-objectives ul {
  margin: 0;
  padding-inline-start: 20px;
  font-size: 14.5px;
}

.content .learning-objectives li {
  margin: 4px 0;
}

.content .lab-challenge {
  margin: 28px 0;
  padding: 4px 22px 18px;
  border: 1px solid var(--ds-border-l2);
  border-radius: var(--ds-radius-lg);
  background: var(--ds-bg-tip);
}

.content .lab-challenge > h2 {
  border-bottom: 0;
  padding-bottom: 0;
}

/* -- print ---------------------------------------------------------------------------------------- */
@media print {
  .navbar,
  .sidebar,
  .toc,
  .pager,
  .code-copy {
    display: none !important;
  }

  .shell {
    display: block;
    padding-top: 0;
  }

  body {
    background: #fff;
    color: #000;
  }
}

/* ==========================================================================
   components.css — search modal, quiz, home/phase cards, 404.
   ========================================================================== */

/* -- theme toggle icon swap -------------------------------------------------- */
.icon-btn .icon-sun { display: none; }
html[data-ds-dark-theme] .icon-btn .icon-sun { display: block; }
html[data-ds-dark-theme] .icon-btn .icon-moon { display: none; }

/* -- search modal ------------------------------------------------------------------ */
.search-dialog {
  width: min(620px, calc(100vw - 32px));
  padding: 0;
  border: 1px solid var(--ds-border-l2);
  border-radius: var(--ds-radius-lg);
  background: var(--ds-bg-layer-2);
  color: var(--ds-label-primary);
  box-shadow: var(--ds-shadow-2);
  overflow: hidden;
}

.search-dialog::backdrop {
  background: var(--ds-bg-mask);
}

.search-head {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 6px 14px;
  border-bottom: 1px solid var(--ds-border-l1);
}

.search-head svg {
  flex: none;
  width: 16px;
  height: 16px;
  color: var(--ds-label-caption);
}

.search-head input {
  flex: 1;
  height: 44px;
  border: 0;
  background: none;
  font: inherit;
  font-size: 15px;
  color: var(--ds-label-primary);
}

.search-head input:focus {
  outline: none;
}

.search-head .search-esc {
  flex: none;
  padding: 2px 7px;
  border: 1px solid var(--ds-border-l2);
  border-radius: 4px;
  font-size: 11px;
  color: var(--ds-label-caption);
}

.search-head .search-close {
  flex: none;
  display: grid;
  place-items: center;
  width: 26px;
  height: 26px;
  border-radius: var(--ds-radius-sm);
  color: var(--ds-label-caption);
  transition: background-color var(--ds-dur-fast) var(--ds-ease),
    color var(--ds-dur-fast) var(--ds-ease);
}

.search-head .search-close:hover {
  background: var(--ds-bg-hover);
  color: var(--ds-label-primary);
}

.search-head .search-close svg {
  width: 15px;
  height: 15px;
}

.search-results {
  max-height: min(420px, 56vh);
  overflow-y: auto;
  padding: 8px;
  margin: 0;
  list-style: none;
}

.search-results li {
  margin: 0;
}

.search-item {
  display: flex;
  flex-direction: column;
  gap: 2px;
  padding: 10px 12px;
  border-radius: var(--ds-radius);
  cursor: pointer;
}

.search-item:hover,
.search-item.selected {
  background: var(--ds-bg-hover);
}

.search-item .s-title {
  font-size: 14px;
  font-weight: 550;
  color: var(--ds-label-primary);
}

.search-item .s-title mark {
  background: none;
  color: var(--ds-accent);
  font-weight: 650;
}

.search-item .s-snippet {
  overflow: hidden;
  font-size: 12px;
  line-height: 1.5;
  color: var(--ds-label-tertiary);
  text-overflow: ellipsis;
  white-space: nowrap;
}

.search-item .s-snippet mark {
  background: none;
  color: var(--ds-accent);
}

.search-item .s-meta {
  font-size: 12px;
  color: var(--ds-label-caption);
}

.search-item .s-meta .s-phase {
  color: var(--ds-label-tertiary);
}

.search-empty {
  padding: 32px 16px;
  text-align: center;
  font-size: 13.5px;
  color: var(--ds-label-tertiary);
}

.search-foot {
  display: flex;
  gap: 14px;
  padding: 8px 14px;
  border-top: 1px solid var(--ds-border-l1);
  font-size: 11.5px;
  color: var(--ds-label-caption);
}

.search-foot kbd {
  padding: 1px 5px;
  border: 1px solid var(--ds-border-l2);
  border-radius: 4px;
  font-size: 10.5px;
  margin-inline-end: 3px;
}

/* -- quiz ------------------------------------------------------------------------------ */
.quiz {
  margin: 44px 0 0;
  border: 1px solid var(--ds-border-l2);
  border-radius: var(--ds-radius-lg);
  background: var(--ds-bg-layer-1);
  overflow: hidden;
}

.quiz-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 14px 20px;
  border-bottom: 1px solid var(--ds-border-l1);
  background: var(--ds-bg-soft);
}

.quiz-title {
  display: flex;
  align-items: center;
  gap: 8px;
  font-size: 15px;
  font-weight: 650;
  color: var(--ds-label-primary);
}

.quiz-title svg {
  width: 16px;
  height: 16px;
  color: var(--ds-accent);
}

.quiz-note {
  font-size: 12px;
  color: var(--ds-label-caption);
}

.quiz-tabs {
  display: flex;
  gap: 4px;
  padding: 10px 14px 0;
}

.quiz-tab {
  padding: 6px 12px;
  border-radius: var(--ds-radius-sm) var(--ds-radius-sm) 0 0;
  font-size: 13px;
  font-weight: 500;
  color: var(--ds-label-tertiary);
  border-bottom: 2px solid transparent;
  transition: color var(--ds-dur-fast) var(--ds-ease),
    border-color var(--ds-dur-fast) var(--ds-ease);
}

.quiz-tab:hover {
  color: var(--ds-label-primary);
}

.quiz-tab[aria-selected='true'] {
  color: var(--ds-accent);
  border-bottom-color: var(--ds-accent);
}

.quiz-body {
  padding: 18px 20px 20px;
}

.quiz-q {
  margin: 0 0 18px;
}

.quiz-q:last-child {
  margin-bottom: 0;
}

.quiz-q .q-text {
  margin: 0 0 10px;
  font-size: 14.5px;
  font-weight: 550;
  color: var(--ds-label-primary);
}

.quiz-q .q-text .q-stage-badge {
  display: inline-block;
  margin-inline-end: 8px;
  padding: 1px 8px;
  border-radius: 999px;
  background: var(--ds-mark-tag);
  font-size: 11px;
  font-weight: 600;
  letter-spacing: 0.02em;
  color: var(--ds-label-tertiary);
  vertical-align: 2px;
}

.quiz-opts {
  display: flex;
  flex-direction: column;
  gap: 8px;
  margin: 0;
  padding: 0;
  list-style: none;
}

.quiz-opt {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  width: 100%;
  padding: 10px 14px;
  border: 1px solid var(--ds-border-l2);
  border-radius: var(--ds-radius);
  background: var(--ds-bg-base);
  color: var(--ds-label-secondary);
  font-size: 14px;
  line-height: 1.6;
  text-align: start;
  transition: border-color var(--ds-dur-fast) var(--ds-ease),
    background-color var(--ds-dur-fast) var(--ds-ease),
    color var(--ds-dur-fast) var(--ds-ease);
}

.quiz-opt:hover:not(:disabled) {
  border-color: var(--ds-border-l4);
  background: var(--ds-bg-hover);
  color: var(--ds-label-primary);
}

.quiz-opt .opt-key {
  flex: none;
  display: grid;
  place-items: center;
  width: 22px;
  height: 22px;
  border-radius: 6px;
  background: var(--ds-mark-tag);
  font-family: var(--ds-font-code);
  font-size: 11.5px;
  font-weight: 600;
  color: var(--ds-label-tertiary);
}

.quiz-opt.correct {
  border-color: var(--ds-success);
  background: var(--ds-success-soft);
  color: var(--ds-label-primary);
}

.quiz-opt.correct::after {
  content: '\2713'; /* ✓ */
  margin-inline-start: auto;
  font-weight: 700;
}

.quiz-opt.correct .opt-key {
  background: var(--ds-success);
  color: var(--ds-label-on-brand);
}

.quiz-opt.wrong {
  border-color: var(--ds-error);
  border-style: dashed;
  background: var(--ds-error-soft);
  color: var(--ds-label-primary);
}

.quiz-opt.wrong::after {
  content: '\2717'; /* ✗ */
  margin-inline-start: auto;
  font-weight: 700;
  color: var(--ds-label-tertiary);
}

.quiz-opt:disabled {
  cursor: default;
  opacity: 0.75;
}

.quiz-opt.correct:disabled,
.quiz-opt.wrong:disabled {
  opacity: 1;
}

.quiz-explain {
  margin: 10px 0 0;
  padding: 10px 14px;
  border-inline-start: 3px solid var(--ds-accent-border);
  border-radius: 0 var(--ds-radius) var(--ds-radius) 0;
  background: var(--ds-bg-soft);
  font-size: 13.5px;
  line-height: 1.7;
  color: var(--ds-label-secondary);
}

.quiz-explain:empty {
  display: none;
}

.quiz-score {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-top: 16px;
  padding-top: 14px;
  border-top: 1px solid var(--ds-border-l1);
  font-size: 13.5px;
  color: var(--ds-label-secondary);
}

.quiz-score .score-line b {
  color: var(--ds-label-primary);
}

.quiz-score .score-line.good b {
  color: var(--ds-success);
}

.quiz-retry {
  padding: 6px 14px;
  border: 1px solid var(--ds-border-l2);
  border-radius: var(--ds-radius-sm);
  font-size: 13px;
  font-weight: 500;
  color: var(--ds-label-primary);
  transition: background-color var(--ds-dur-fast) var(--ds-ease),
    border-color var(--ds-dur-fast) var(--ds-ease);
}

.quiz-retry:hover {
  background: var(--ds-bg-hover);
  border-color: var(--ds-border-l4);
}

/* -- home page --------------------------------------------------------------------------- */
.home-hero {
  padding: 72px 0 56px;
  text-align: center;
}

.home-hero .hero-kicker {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 4px 14px;
  border: 1px solid var(--ds-accent-border);
  border-radius: 999px;
  background: var(--ds-accent-soft);
  font-size: 13px;
  font-weight: 550;
  color: var(--ds-accent-ink);
}

.home-hero h1 {
  margin: 20px 0 14px;
  font-size: 44px;
  line-height: 1.15;
  font-weight: 750;
  letter-spacing: -0.025em;
}

html[lang='zh'] .home-hero h1 {
  letter-spacing: 0;
}

.home-hero .hero-sub {
  max-width: 620px;
  margin: 0 auto 28px;
  font-size: 17px;
  line-height: 1.75;
  color: var(--ds-label-secondary);
}

.home-hero .hero-cta {
  display: flex;
  justify-content: center;
  gap: 12px;
  flex-wrap: wrap;
}

.home-stats {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
  max-width: min(var(--ds-content-w), 100%);
  margin: 0 auto 24px;
}

.stat-card {
  padding: 18px 12px;
  border: 1px solid var(--ds-border-l1);
  border-radius: var(--ds-radius-lg);
  background: var(--ds-bg-layer-1);
  text-align: center;
}

.stat-card .stat-num {
  font-size: 26px;
  font-weight: 700;
  font-variant-numeric: tabular-nums;
  color: var(--ds-label-primary);
  letter-spacing: -0.02em;
}

.stat-card .stat-label {
  margin-top: 2px;
  font-size: 12.5px;
  color: var(--ds-label-tertiary);
}

/* phase grid */
.section-head {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 12px;
  margin: 48px 0 18px;
}

.section-head h2 {
  margin: 0;
  font-size: 22px;
  font-weight: 650;
  letter-spacing: -0.01em;
}

.section-head .section-link {
  font-size: 13.5px;
}

.phase-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(240px, 1fr));
  gap: 12px;
}

.phase-card {
  display: flex;
  flex-direction: column;
  gap: 6px;
  padding: 18px;
  border: 1px solid var(--ds-border-l1);
  border-radius: var(--ds-radius-lg);
  background: var(--ds-bg-layer-1);
  color: var(--ds-label-primary);
  transition: border-color var(--ds-dur-fast) var(--ds-ease),
    box-shadow var(--ds-dur) var(--ds-ease),
    transform var(--ds-dur) var(--ds-ease);
}

.phase-card:hover {
  border-color: var(--ds-border-l3);
  box-shadow: var(--ds-shadow-1);
  transform: translateY(-1px);
  color: var(--ds-label-primary);
  text-decoration: none;
}

.phase-card .pc-top {
  display: flex;
  align-items: center;
  gap: 10px;
}

.phase-card .pc-num {
  display: grid;
  place-items: center;
  min-width: 34px;
  height: 34px;
  border-radius: var(--ds-radius);
  background: var(--ds-mark-tag);
  font-family: var(--ds-font-code);
  font-size: 13px;
  font-weight: 650;
  color: var(--ds-label-secondary);
}

.phase-card:hover .pc-num {
  background: var(--ds-accent);
  color: var(--ds-label-on-brand);
}

.phase-card .pc-title {
  font-size: 15px;
  font-weight: 620;
  line-height: 1.4;
}

.phase-card .pc-meta {
  font-size: 12.5px;
  color: var(--ds-label-tertiary);
  font-variant-numeric: tabular-nums;
}

.home-how {
  margin: 56px 0 0;
  padding: 24px 28px;
  border: 1px solid var(--ds-border-l1);
  border-radius: var(--ds-radius-lg);
  background: var(--ds-bg-soft);
}

.home-how h2 {
  margin: 0 0 10px;
  font-size: 18px;
  font-weight: 650;
}

.home-how ol {
  margin: 0;
  padding-inline-start: 22px;
  color: var(--ds-label-secondary);
  font-size: 14.5px;
}

.home-how li {
  margin: 6px 0;
}

/* -- phase landing ------------------------------------------------------------------------- */
.phase-hero {
  margin-bottom: 28px;
}

.phase-hero .phase-tag {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 3px 12px;
  border-radius: 999px;
  background: var(--ds-mark-tag);
  font-family: var(--ds-font-code);
  font-size: 12px;
  font-weight: 600;
  color: var(--ds-label-tertiary);
}

.phase-hero h1 {
  margin: 12px 0 8px;
  font-size: 32px;
  font-weight: 700;
  letter-spacing: -0.02em;
}

.phase-hero .phase-hook {
  max-width: 640px;
  margin: 0;
  font-size: 15.5px;
  color: var(--ds-label-secondary);
}

.lesson-list {
  border: 1px solid var(--ds-border-l1);
  border-radius: var(--ds-radius-lg);
  overflow: hidden;
}

.lesson-row {
  display: flex;
  align-items: center;
  gap: 14px;
  padding: 13px 18px;
  color: var(--ds-label-primary);
  background: var(--ds-bg-layer-1);
  border-bottom: 1px solid var(--ds-border-l1);
  transition: background-color var(--ds-dur-fast) var(--ds-ease);
  min-height: 44px;
}

.lesson-row:last-child {
  border-bottom: 0;
}

.lesson-row:hover {
  background: var(--ds-bg-hover);
  color: var(--ds-label-primary);
  text-decoration: none;
}

.lesson-row .lr-num {
  flex: none;
  width: 34px;
  font-family: var(--ds-font-code);
  font-size: 12px;
  color: var(--ds-label-caption);
  font-variant-numeric: tabular-nums;
}

.lesson-row .lr-title {
  flex: 1;
  min-width: 0;
  font-size: 14.5px;
  font-weight: 500;
}

.lesson-row:hover .lr-title {
  color: var(--ds-accent);
}

.lesson-row .lr-badges {
  flex: none;
  display: flex;
  align-items: center;
  gap: 8px;
}

.lr-badge {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  padding: 2px 9px;
  border-radius: 999px;
  background: var(--ds-mark-tag);
  font-size: 11.5px;
  color: var(--ds-label-tertiary);
  white-space: nowrap;
}

.lr-badge svg {
  width: 12px;
  height: 12px;
}

.lr-badge.type-build { background: var(--ds-accent-soft); color: var(--ds-accent-ink); }

@media (max-width: 767px) {
  .home-stats {
    grid-template-columns: repeat(2, 1fr);
  }

  .home-hero h1 {
    font-size: 32px;
  }

  .lesson-row .lr-badges .lr-badge.time {
    display: none;
  }
}

/* -- negotiation / 404 ----------------------------------------------------------------------- */
.center-page {
  min-height: 70vh;
  display: grid;
  place-items: center;
  padding: 48px 20px;
  text-align: center;
}

.center-page .center-box {
  max-width: 480px;
}

.center-page h1 {
  font-size: 34px;
  font-weight: 700;
  letter-spacing: -0.02em;
  margin: 0 0 12px;
}

.center-page p {
  color: var(--ds-label-secondary);
  margin: 0 0 24px;
}

.center-page .lang-choice {
  display: flex;
  justify-content: center;
  gap: 12px;
  flex-wrap: wrap;
}

.code-404 {
  font-family: var(--ds-font-code);
  font-size: 64px;
  font-weight: 700;
  letter-spacing: 0.06em;
  background: linear-gradient(135deg, var(--ds-accent), var(--dsw-deepseek-300));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
  margin-bottom: 4px;
}

/* ==========================================================================
   Learning map page (/learning-paths) — role-based routes, monochrome.
   ========================================================================== */
.paths-page .path-jump {
  display: flex;
  flex-wrap: wrap;
  gap: 6px 10px;
  margin: 0 0 28px;
}

.paths-page .path-jump a {
  padding: 4px 12px;
  border: 1px solid var(--ds-border-l2);
  border-radius: 999px;
  font-size: 13px;
  color: var(--ds-label-secondary);
  text-decoration: none;
  transition: background-color var(--ds-dur-fast) var(--ds-ease),
    color var(--ds-dur-fast) var(--ds-ease);
}

.paths-page .path-jump a:hover,
.paths-page .path-jump a:focus-visible {
  background: var(--ds-bg-hover);
  color: var(--ds-label-primary);
}

.paths-page .path-card {
  margin: 0 0 32px;
  padding: 24px 26px 18px;
  border: 1px solid var(--ds-border-l1);
  border-radius: var(--ds-radius-lg);
  background: var(--ds-bg-base);
}

.paths-page .path-head h2 {
  margin: 0;
  padding: 0;
  border-bottom: 0;
  font-size: 21px;
  font-weight: 650;
  letter-spacing: -0.01em;
}

.paths-page .path-title-en {
  margin: 2px 0 0;
  font-size: 12.5px;
  color: var(--ds-label-caption);
}

.paths-page .path-decision {
  margin: 10px 0 0;
  font-size: 14.5px;
  color: var(--ds-label-primary);
}

.paths-page .path-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  margin-top: 12px;
}

.paths-page .path-chip {
  padding: 2px 10px;
  border: 1px solid var(--ds-border-l2);
  border-radius: 999px;
  background: var(--ds-mark-tag);
  font-size: 12px;
  font-variant-numeric: tabular-nums;
  color: var(--ds-label-secondary);
}

.paths-page .path-summary {
  margin: 14px 0 0;
  font-size: 14.5px;
  line-height: 1.7;
  color: var(--ds-label-secondary);
}

.paths-page .path-card h3 {
  margin: 22px 0 8px;
  font-size: 14px;
  font-weight: 650;
  color: var(--ds-label-primary);
}

.paths-page .path-list {
  margin: 0 0 8px;
  padding-inline-start: 20px;
}

.paths-page .path-list li {
  margin: 5px 0;
  font-size: 14px;
  line-height: 1.65;
  color: var(--ds-label-secondary);
}

.paths-page .path-list li strong {
  color: var(--ds-label-primary);
  font-weight: 600;
}

.paths-page .path-portfolio {
  margin: 18px 0 6px;
  padding: 12px 16px;
  border: 1px solid var(--ds-border-l2);
  border-inline-start: 3px solid var(--ds-accent);
  border-radius: 0 var(--ds-radius) var(--ds-radius) 0;
  background: var(--ds-bg-soft);
}

.paths-page .path-portfolio h3 {
  margin: 0 0 6px;
}

.paths-page .path-portfolio p {
  margin: 0;
  font-size: 14px;
  line-height: 1.65;
  color: var(--ds-label-secondary);
}

.paths-page .path-stage-title {
  padding-top: 14px;
  border-top: 1px solid var(--ds-border-l1);
}

.paths-page .path-stage-outcome {
  margin: 0 0 10px;
  font-size: 13.5px;
  color: var(--ds-label-caption);
}

.paths-page .path-artifact {
  margin: 8px 0 0;
  font-size: 13.5px;
  color: var(--ds-label-caption);
}

.paths-page .path-lessons {
  margin: 8px 0 10px;
  padding: 0;
  list-style: none;
}

.paths-page .path-lessons li {
  margin: 0;
}

.paths-page .path-lessons a {
  display: flex;
  align-items: baseline;
  gap: 10px;
  padding: 6px 10px;
  border-radius: var(--ds-radius-sm);
  font-size: 14px;
  text-decoration: none;
  color: var(--ds-label-primary);
  transition: background-color var(--ds-dur-fast) var(--ds-ease);
}

.paths-page .path-lessons a:hover,
.paths-page .path-lessons a:focus-visible {
  background: var(--ds-bg-hover);
}

.paths-page .path-lesson-num {
  flex: none;
  min-width: 30px;
  font-family: var(--ds-font-code);
  font-size: 12px;
  color: var(--ds-label-caption);
  font-variant-numeric: tabular-nums;
}

.paths-page .path-lesson-title {
  flex: 1;
  min-width: 0;
}

.paths-page .path-lesson-min {
  flex: none;
  font-family: var(--ds-font-code);
  font-size: 12px;
  color: var(--ds-label-caption);
  font-variant-numeric: tabular-nums;
}

/* lesson-diagrams.css — gallery of a lesson's asset SVGs, appended to the
 * article by convention (assets/*.svg are unreferenced upstream; build.js
 * collects them). Visual language mirrors the interactive-figure chrome (.lf
 * in vendor/figures/lesson-figures.js): same tokens, so dark theme follows. */
.content .lesson-diagrams {
  border: 1px solid var(--rule-soft, #ddd);
  background: var(--bg, #fafafa);
  margin: 28px 0;
}

.content .lesson-diagrams-head {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  gap: 12px;
  margin: 0;
  padding: 12px 16px;
  border-bottom: 1px solid var(--rule-soft, #ddd);
  font-family: var(--font-mono, monospace);
  font-size: 0.68rem;
  line-height: 1.4;
  font-weight: 600;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--blueprint, #595959);
}

.content .lesson-diagrams-count {
  color: var(--ink-mute, #777);
  font-weight: 400;
  white-space: nowrap;
}

.content .lesson-diagrams-body {
  padding: 16px;
}

.content .lesson-diagrams figure {
  margin: 0;
}

.content .lesson-diagrams figure + figure {
  margin-top: 20px;
  padding-top: 20px;
  border-top: 1px dashed var(--rule-soft, #ddd);
}

/* SVG line art keeps a paper-white card in both themes — the assets are drawn
 * for light backgrounds, so the theme-aware .content img background (which
 * goes dark) would make black strokes unreadable. */
.content .lesson-diagrams img {
  max-width: 100%;
  height: auto;
  background: #fff;
}

html[data-ds-dark-theme] .content .lesson-diagrams img {
  background: #fff;
}

.content .lesson-diagrams figcaption {
  font-family: var(--font-mono, monospace);
  font-size: 0.7rem;
  letter-spacing: 0.04em;
  text-align: center;
  color: var(--ink-mute, #777);
  margin-top: 10px;
}