/* ============================================================
   AI × CAD 学习与工作指南 — shared design system
   "Blueprint" : editorial + engineering + AI gradient
   ============================================================ */

:root {
  /* ─── color tokens : light (paper) ─────────────────────── */
  --paper:        #F1EEE6;
  --paper-2:      #E9E4D8;
  --paper-edge:   #DDD5C3;
  --ink:          #0B1726;
  --ink-2:        #2A3A52;
  --ink-3:        #5A6B82;
  --blue:         #18468F;
  --blue-2:       #2C66C7;
  --blue-deep:    #0B2956;
  --cyan:         #0E9BC4;
  --coral:        #E85D2F;     /* AI accent — used sparingly */
  --rule:         rgba(11, 23, 38, 0.10);
  --rule-strong:  rgba(11, 23, 38, 0.22);
  --grid-line:    rgba(24, 70, 143, 0.07);
  --grid-major:   rgba(24, 70, 143, 0.12);
  --tag-bg:       rgba(24, 70, 143, 0.07);
  --tag-bg-2:     rgba(232, 93, 47, 0.10);
  --card:         #FAF8F2;
  --card-edge:    rgba(11, 23, 38, 0.08);
  --code-bg:      #0E1A2B;
  --code-ink:     #E8E4D4;

  /* ─── type ─────────────────────────────────────────────── */
  --f-serif:  "Noto Serif SC", "Source Han Serif SC", "Songti SC", Georgia, serif;
  --f-sans:   "Noto Sans SC", "PingFang SC", "HarmonyOS Sans", -apple-system, system-ui, sans-serif;
  --f-mono:   "JetBrains Mono", "IBM Plex Mono", "SF Mono", ui-monospace, monospace;

  /* ─── geometry ─────────────────────────────────────────── */
  --container:    1320px;
  --gutter:       clamp(24px, 4vw, 56px);
  --section-y:    clamp(80px, 11vw, 160px);
  --radius:       2px;        /* engineering — sharp */
  --radius-soft:  10px;       /* for AI-ish cards */
}

[data-theme="dark"] {
  --paper:        #0A1320;
  --paper-2:      #0F1B2D;
  --paper-edge:   #182740;
  --ink:          #ECE6D6;
  --ink-2:        #BCC6D6;
  --ink-3:        #7E8AA0;
  --blue:         #6BA0F0;
  --blue-2:       #8EBAF7;
  --blue-deep:    #BCD3F5;
  --cyan:         #36C2E8;
  --coral:        #FF7A52;
  --rule:         rgba(236, 230, 214, 0.10);
  --rule-strong:  rgba(236, 230, 214, 0.22);
  --grid-line:    rgba(107, 160, 240, 0.07);
  --grid-major:   rgba(107, 160, 240, 0.14);
  --tag-bg:       rgba(107, 160, 240, 0.10);
  --tag-bg-2:     rgba(255, 122, 82, 0.13);
  --card:         #11203A;
  --card-edge:    rgba(236, 230, 214, 0.08);
  --code-bg:      #04101F;
  --code-ink:     #DCE5F3;
}

/* ─── reset ────────────────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; scroll-behavior: smooth; }
body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--f-sans);
  font-size: 16px;
  line-height: 1.6;
  font-feature-settings: "tnum", "ss01";
  text-rendering: optimizeLegibility;
  -webkit-font-smoothing: antialiased;
  transition: background-color 0.3s ease, color 0.3s ease;
}
a { color: inherit; text-decoration: none; }
button { font: inherit; color: inherit; background: none; border: 0; padding: 0; cursor: pointer; }
img, svg { display: block; max-width: 100%; }
hr { border: 0; border-top: 1px solid var(--rule); margin: 0; }

::selection { background: var(--blue); color: var(--paper); }

/* ─── blueprint grid background (subtle) ───────────────── */
.bg-grid {
  position: relative;
  isolation: isolate;
}
.bg-grid::before {
  content: "";
  position: absolute; inset: 0;
  background-image:
    linear-gradient(to right, var(--grid-line) 1px, transparent 1px),
    linear-gradient(to bottom, var(--grid-line) 1px, transparent 1px),
    linear-gradient(to right, var(--grid-major) 1px, transparent 1px),
    linear-gradient(to bottom, var(--grid-major) 1px, transparent 1px);
  background-size: 32px 32px, 32px 32px, 160px 160px, 160px 160px;
  pointer-events: none;
  z-index: -1;
  mask-image: linear-gradient(to bottom, rgba(0,0,0,0.7), rgba(0,0,0,0.2));
}

/* ─── layout primitives ────────────────────────────────── */
.container {
  width: 100%;
  max-width: var(--container);
  margin: 0 auto;
  padding-left: var(--gutter);
  padding-right: var(--gutter);
}

section { position: relative; }

/* section label — "/ 01  FOUNDATIONS" */
.section-head {
  display: flex;
  align-items: baseline;
  gap: 16px;
  padding: 14px 0;
  margin-bottom: 32px;
  border-top: 1px solid var(--ink);
  border-bottom: 1px solid var(--rule);
}
.section-head .num {
  font-family: var(--f-mono);
  font-size: 12px;
  font-weight: 500;
  letter-spacing: 0.08em;
  color: var(--ink);
}
.section-head .label {
  font-family: var(--f-mono);
  font-size: 11px;
  font-weight: 500;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--ink-3);
}
.section-head .crumb {
  margin-left: auto;
  font-family: var(--f-mono);
  font-size: 11px;
  letter-spacing: 0.12em;
  color: var(--ink-3);
  text-transform: uppercase;
}

/* ─── type scale ───────────────────────────────────────── */
.eyebrow {
  font-family: var(--f-mono);
  font-size: 11px;
  font-weight: 500;
  letter-spacing: 0.22em;
  text-transform: uppercase;
  color: var(--ink-3);
}
.display {
  font-family: var(--f-serif);
  font-weight: 700;
  font-size: clamp(48px, 9vw, 124px);
  line-height: 0.92;
  letter-spacing: -0.02em;
  margin: 0;
}
.display .quiet {
  color: var(--ink-3);
  font-weight: 400;
  font-style: italic;
}
.h1 {
  font-family: var(--f-serif);
  font-weight: 700;
  font-size: clamp(40px, 6vw, 72px);
  line-height: 1.04;
  letter-spacing: -0.015em;
  margin: 0;
}
.h2 {
  font-family: var(--f-serif);
  font-weight: 600;
  font-size: clamp(28px, 3.4vw, 44px);
  line-height: 1.15;
  letter-spacing: -0.01em;
  margin: 0;
}
.h3 {
  font-family: var(--f-sans);
  font-weight: 600;
  font-size: clamp(20px, 2vw, 24px);
  line-height: 1.3;
  margin: 0;
}
.lede {
  font-family: var(--f-serif);
  font-size: clamp(20px, 1.9vw, 26px);
  line-height: 1.45;
  font-weight: 400;
  color: var(--ink-2);
  max-width: 38ch;
}
.body { font-size: 16px; line-height: 1.7; color: var(--ink-2); }
.small { font-size: 13px; color: var(--ink-3); }
.mono  { font-family: var(--f-mono); letter-spacing: 0.02em; }

/* ─── nav ──────────────────────────────────────────────── */
.nav {
  position: sticky; top: 0; z-index: 50;
  background: color-mix(in oklab, var(--paper) 88%, transparent);
  backdrop-filter: saturate(140%) blur(12px);
  -webkit-backdrop-filter: saturate(140%) blur(12px);
  border-bottom: 1px solid var(--rule);
}
.nav-inner {
  display: flex; align-items: center; gap: 36px;
  height: 64px;
}
.brand {
  display: flex; align-items: center; gap: 12px;
}
.brand-mark {
  width: 32px; height: 32px;
  display: grid; place-items: center;
  border: 1.5px solid var(--ink);
  border-radius: var(--radius);
  position: relative;
}
.brand-mark::before, .brand-mark::after {
  content: "";
  position: absolute;
  background: var(--ink);
}
.brand-mark::before { left: -4px; right: -4px; top: 50%; height: 1px; }
.brand-mark::after  { top: -4px; bottom: -4px; left: 50%; width: 1px; }
.brand-mark span {
  font-family: var(--f-serif); font-weight: 700;
  font-size: 18px; line-height: 1;
  background: var(--paper); padding: 2px 3px;
  position: relative; z-index: 1;
}
.brand-name {
  font-family: var(--f-serif);
  font-weight: 700;
  font-size: 17px;
  letter-spacing: 0.02em;
  white-space: nowrap;
}
.brand-name small {
  display: block;
  font-family: var(--f-mono);
  font-size: 9.5px;
  font-weight: 500;
  letter-spacing: 0.18em;
  color: var(--ink-3);
  text-transform: uppercase;
  margin-top: 1px;
}

.nav-links {
  display: flex; align-items: center; gap: 4px;
  margin-left: auto;
}
.nav-link {
  position: relative;
  padding: 8px 14px;
  font-size: 14px;
  font-weight: 500;
  color: var(--ink-2);
  border-radius: var(--radius);
  transition: color 0.15s;
}
.nav-link::before {
  content: attr(data-num);
  font-family: var(--f-mono);
  font-size: 9px;
  font-weight: 500;
  letter-spacing: 0.1em;
  color: var(--ink-3);
  margin-right: 6px;
  vertical-align: 2px;
}
.nav-link:hover { color: var(--ink); }
.nav-link.is-active { color: var(--ink); }
.nav-link.is-active::after {
  content: ""; position: absolute;
  left: 14px; right: 14px; bottom: 2px;
  height: 1.5px; background: var(--blue);
}

.theme-toggle {
  display: inline-grid; place-items: center;
  width: 36px; height: 36px;
  border: 1px solid var(--rule-strong);
  border-radius: var(--radius);
  transition: background 0.15s, border-color 0.15s;
}
.theme-toggle:hover { background: var(--tag-bg); border-color: var(--blue); }
.theme-toggle svg { width: 16px; height: 16px; }
.theme-toggle .icon-sun { display: none; }
.theme-toggle .icon-moon { display: block; }
[data-theme="dark"] .theme-toggle .icon-sun  { display: block; }
[data-theme="dark"] .theme-toggle .icon-moon { display: none; }

/* mobile nav */
.nav-burger { display: none; }
@media (max-width: 880px) {
  .nav-links { display: none; }
  .nav-links.is-open {
    display: flex; flex-direction: column; gap: 0;
    position: absolute; top: 64px; left: 0; right: 0;
    background: var(--paper);
    border-bottom: 1px solid var(--rule);
    padding: 12px 0;
  }
  .nav-links.is-open .nav-link {
    padding: 14px var(--gutter);
    border-radius: 0;
    border-top: 1px solid var(--rule);
  }
  .nav-burger {
    display: inline-grid; place-items: center;
    width: 36px; height: 36px;
    border: 1px solid var(--rule-strong); border-radius: var(--radius);
    margin-left: auto;
  }
  .nav-burger + .theme-toggle { margin-left: 8px; }
}

/* ─── buttons ──────────────────────────────────────────── */
.btn {
  display: inline-flex; align-items: center; gap: 10px;
  padding: 14px 22px;
  font-size: 14px; font-weight: 600;
  letter-spacing: 0.02em;
  border-radius: var(--radius);
  border: 1px solid transparent;
  transition: transform 0.15s, background 0.15s, border-color 0.15s, color 0.15s;
  cursor: pointer;
}
.btn .arr { transition: transform 0.2s; }
.btn:hover .arr { transform: translateX(4px); }
.btn-primary {
  background: var(--ink);
  color: var(--paper);
}
.btn-primary:hover { background: var(--blue-deep); }
[data-theme="dark"] .btn-primary { background: var(--ink); color: var(--paper); }
[data-theme="dark"] .btn-primary:hover { background: var(--blue); color: var(--paper); }

.btn-ghost {
  border-color: var(--rule-strong);
  color: var(--ink);
}
.btn-ghost:hover { border-color: var(--blue); color: var(--blue); }

.btn-link {
  padding: 0;
  font-family: var(--f-mono);
  font-size: 12px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--ink);
  border-bottom: 1px solid var(--ink);
  border-radius: 0;
  padding-bottom: 2px;
}
.btn-link:hover { color: var(--blue); border-color: var(--blue); }

/* ─── tags / badges ────────────────────────────────────── */
.tag {
  display: inline-flex; align-items: center; gap: 6px;
  padding: 4px 10px;
  font-family: var(--f-mono);
  font-size: 10.5px; font-weight: 500;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  background: var(--tag-bg);
  color: var(--blue);
  border-radius: 100px;
  white-space: nowrap;
}
.tag.coral { background: var(--tag-bg-2); color: var(--coral); }
.tag.plain { background: transparent; color: var(--ink-3); padding-left: 0; padding-right: 0; }
.tag.outline { background: transparent; border: 1px solid var(--rule-strong); color: var(--ink-2); }

/* ─── card ─────────────────────────────────────────────── */
.card {
  position: relative;
  background: var(--card);
  border: 1px solid var(--card-edge);
  border-radius: var(--radius);
  padding: 28px;
  transition: border-color 0.2s, transform 0.2s;
}
.card-hover { transition: transform 0.25s, border-color 0.25s, box-shadow 0.25s; }
.card-hover:hover {
  border-color: var(--blue);
  transform: translateY(-2px);
}

/* corner crosshairs on important cards */
.crosshair {
  position: relative;
}
.crosshair::before, .crosshair::after {
  content: ""; position: absolute;
  width: 14px; height: 14px;
  border: 1px solid var(--ink-2);
}
.crosshair::before {
  top: -5px; left: -5px;
  border-right: 0; border-bottom: 0;
}
.crosshair::after {
  bottom: -5px; right: -5px;
  border-left: 0; border-top: 0;
}

/* ─── ascii / dimension rule ───────────────────────────── */
.dim-rule {
  display: flex; align-items: center; gap: 12px;
  font-family: var(--f-mono);
  font-size: 10.5px;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--ink-3);
}
.dim-rule::before, .dim-rule::after {
  content: ""; flex: 1;
  height: 1px;
  background: linear-gradient(to right, transparent, var(--rule-strong) 8px, var(--rule-strong) calc(100% - 8px), transparent);
}
.dim-rule::before { background: linear-gradient(to right, transparent, var(--rule-strong) 8px, var(--rule-strong)); }
.dim-rule::after  { background: linear-gradient(to left,  transparent, var(--rule-strong) 8px, var(--rule-strong)); }

/* ─── footer ───────────────────────────────────────────── */
.footer {
  margin-top: var(--section-y);
  padding: 56px 0 32px;
  border-top: 1px solid var(--rule-strong);
}
.footer-grid {
  display: grid;
  grid-template-columns: 2fr repeat(3, 1fr);
  gap: 48px;
  margin-bottom: 48px;
}
.footer h4 {
  font-family: var(--f-mono);
  font-size: 11px;
  font-weight: 500;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--ink-3);
  margin: 0 0 16px;
}
.footer ul { list-style: none; padding: 0; margin: 0; display: grid; gap: 10px; }
.footer a { color: var(--ink-2); font-size: 14px; }
.footer a:hover { color: var(--blue); }
.footer-bottom {
  display: flex; justify-content: space-between; align-items: center;
  padding-top: 24px;
  border-top: 1px solid var(--rule);
  font-family: var(--f-mono);
  font-size: 11px;
  letter-spacing: 0.12em;
  color: var(--ink-3);
  text-transform: uppercase;
}
@media (max-width: 720px) {
  .footer-grid { grid-template-columns: 1fr 1fr; }
}

/* ─── ai gradient + shapes ─────────────────────────────── */
.ai-blob {
  position: absolute;
  border-radius: 50%;
  filter: blur(60px);
  opacity: 0.55;
  pointer-events: none;
  mix-blend-mode: multiply;
}
[data-theme="dark"] .ai-blob { mix-blend-mode: screen; opacity: 0.35; }
.ai-blob.blue  { background: radial-gradient(circle, var(--blue) 0%, transparent 70%); }
.ai-blob.cyan  { background: radial-gradient(circle, var(--cyan) 0%, transparent 70%); }
.ai-blob.coral { background: radial-gradient(circle, var(--coral) 0%, transparent 70%); }

/* ─── code block ───────────────────────────────────────── */
.code {
  font-family: var(--f-mono);
  font-size: 13px;
  line-height: 1.65;
  background: var(--code-bg);
  color: var(--code-ink);
  padding: 20px 22px;
  border-radius: var(--radius);
  overflow-x: auto;
  border: 1px solid rgba(255,255,255,0.04);
}
.code .var  { color: #FFB877; }
.code .com  { color: #6B7E9A; font-style: italic; }
.code .kw   { color: #7CC1F0; }
.code .str  { color: #A6E22E; }

/* ─── accessibility ────────────────────────────────────── */
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
}

/* ─── utilities ────────────────────────────────────────── */
.flex { display: flex; }
.col  { display: flex; flex-direction: column; }
.gap-2 { gap: 8px; } .gap-3 { gap: 12px; } .gap-4 { gap: 16px; }
.gap-6 { gap: 24px; } .gap-8 { gap: 32px; }
.mt-2 { margin-top: 8px; }  .mt-4 { margin-top: 16px; }
.mt-6 { margin-top: 24px; } .mt-8 { margin-top: 32px; }
.mt-12 { margin-top: 48px; } .mt-16 { margin-top: 64px; }
.mb-4 { margin-bottom: 16px; } .mb-6 { margin-bottom: 24px; }
.text-center { text-align: center; }
.muted { color: var(--ink-3); }
.ink-2 { color: var(--ink-2); }
.wrap-balance { text-wrap: balance; }
.wrap-pretty { text-wrap: pretty; }