:root {
  --color-paper: oklch(97.5% 0.012 105);
  --color-surface: oklch(99% 0.006 105);
  --color-paper-2: oklch(94.5% 0.015 105);
  --color-ink: oklch(27% 0.025 160);
  --color-muted: oklch(48% 0.018 160);
  --color-rule: oklch(86% 0.014 130);
  --color-accent: oklch(43% 0.085 165);
  --color-accent-ink: oklch(99% 0.006 105);
  --color-tint: oklch(93% 0.031 158);
  --color-go: oklch(43% 0.074 240);
  --color-go-tint: oklch(94% 0.022 240);
  --color-warm: oklch(48% 0.092 55);
  --color-warm-tint: oklch(94% 0.032 85);
  --color-code: oklch(24% 0.024 160);
  --color-code-ink: oklch(94% 0.021 145);
  --color-error: oklch(46% 0.16 30);
  --color-error-tint: oklch(96% 0.02 30);
  --color-focus: oklch(54% 0.17 65);
  --color-transparent: transparent;
  --font-display: "Noto Serif SC", "Songti SC", "STSong", "SimSun", serif;
  --font-body: "IBM Plex Sans", "PingFang SC", "Microsoft YaHei", sans-serif;
  --font-code: "JetBrains Mono", "Cascadia Code", monospace;
  --space-xs: 4px;
  --space-sm: 8px;
  --space-md: 12px;
  --space-lg: 16px;
  --space-xl: 24px;
  --space-2xl: 32px;
  --space-3xl: 48px;
  --space-4xl: 64px;
  --text-xs: 0.75rem;
  --text-sm: 0.875rem;
  --text-base: 1rem;
  --text-md: 1.25rem;
  --text-lg: 1.563rem;
  --text-xl: 1.953rem;
  --text-display: clamp(1.9rem, 2.2vw + 1rem, 3rem);
  --radius-sm: 6px;
  --radius-md: 12px;
  --radius-lg: 18px;
  --rule-width: 1px;
  --ease-out: cubic-bezier(0.22, 1, 0.36, 1);
  --ease-in: cubic-bezier(0.55, 0, 1, 0.45);
  --ease-in-out: cubic-bezier(0.65, 0, 0.35, 1);
  --dur-fast: 140ms;
  --dur-base: 220ms;
}

/* Approved workbook theme: shared by every production route. */
:root {
  --color-paper: #faf9f5;
  --color-surface: #fdfcf9;
  --color-paper-2: #f2f0e9;
  --color-ink: #302e2b;
  --color-muted: #706c65;
  --color-rule: #dedbd2;
  --color-accent: #9b4c34;
  --color-accent-ink: #faf9f5;
  --color-tint: #eee2d9;
  --color-code: #eeece5;
  --color-code-ink: #302e2b;
  --color-focus: #8b4b37;
  --color-overlay: #25221c60;
  --font-display: Georgia, "Noto Serif SC", "Songti SC", "STSong", "SimSun", serif;
  --font-body: "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
  --radius-sm: 7px;
  --radius-md: 10px;
  --radius-lg: 14px;
  --text-display: clamp(1.8rem, 2.3vw, 2.4rem);
  --rail-width: 224px;
  --assistant-width: 354px;
}