/* ============================================================
   控制论读书站 · 全站样式
   视觉方向：印刷蓝 × 工程图纸 × 80年代科普读物
   ============================================================ */

:root {
  --paper: #fafaf7;
  --paper-deep: #f1f1ec;
  --ink: #1b1c1e;
  --muted: #5c6470;
  --blue: #2b4c9b;
  --blue-deep: #1e3a75;
  --blue-wash: #e8edf7;
  --red: #be3b2c;
  --line: #d8dee6;
  --grid: rgba(43, 76, 155, 0.08);
  --serif: "Songti SC", "Noto Serif SC", "STSong", serif;
  --sans: -apple-system, "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  --mono: "SF Mono", ui-monospace, "Menlo", monospace;
}

* { margin: 0; padding: 0; box-sizing: border-box; }

html { scroll-behavior: smooth; }
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { animation: none !important; transition: none !important; }
}

body {
  font-family: var(--sans);
  background: var(--paper);
  color: var(--ink);
  line-height: 1.85;
  font-size: 16px;
}

/* ---------- 导航 ---------- */
.nav {
  position: sticky;
  top: 0;
  z-index: 50;
  background: rgba(250, 250, 247, 0.94);
  backdrop-filter: blur(8px);
  border-bottom: 2px solid var(--ink);
}
.nav-inner {
  max-width: 1080px;
  margin: 0 auto;
  padding: 0 24px;
  display: flex;
  align-items: center;
  gap: 28px;
  height: 58px;
}
.nav-brand {
  font-family: var(--mono);
  font-size: 13px;
  letter-spacing: 0.14em;
  color: var(--ink);
  text-decoration: none;
  font-weight: 700;
  white-space: nowrap;
}
.nav-brand .loop-mark { color: var(--blue); }
.nav-links {
  display: flex;
  gap: 4px;
  margin-left: auto;
  overflow-x: auto;
}
.nav-links a {
  font-size: 14px;
  color: var(--muted);
  text-decoration: none;
  padding: 6px 12px;
  border-radius: 3px;
  white-space: nowrap;
}
.nav-links a:hover { color: var(--blue-deep); background: var(--blue-wash); }
.nav-links a.active {
  color: var(--paper);
  background: var(--blue);
}

/* ---------- 版面骨架 ---------- */
.wrap { max-width: 1080px; margin: 0 auto; padding: 0 24px; }
.prose { max-width: 760px; }

section { padding: 72px 0; }
section + section { border-top: 1px solid var(--line); }

.eyebrow {
  font-family: var(--mono);
  font-size: 12px;
  letter-spacing: 0.22em;
  color: var(--blue);
  text-transform: uppercase;
  margin-bottom: 14px;
}
h1, h2, h3 { font-family: var(--serif); font-weight: 900; line-height: 1.3; }
h1 { font-size: clamp(34px, 5.5vw, 56px); letter-spacing: 0.02em; }
h2 { font-size: clamp(26px, 3.6vw, 36px); margin-bottom: 20px; }
h3 { font-size: 20px; margin: 28px 0 10px; }
p { margin: 14px 0; }
.lede { font-size: 18px; color: var(--muted); max-width: 680px; }
strong { color: var(--blue-deep); }
em { font-style: normal; border-bottom: 2px solid var(--red); }

a.text-link { color: var(--blue); text-decoration: underline; text-underline-offset: 3px; }

blockquote {
  border-left: 3px solid var(--blue);
  background: var(--blue-wash);
  padding: 16px 22px;
  margin: 22px 0;
  font-family: var(--serif);
  font-size: 17px;
}
blockquote cite {
  display: block;
  font-family: var(--mono);
  font-size: 12px;
  color: var(--muted);
  margin-top: 8px;
  font-style: normal;
}

/* ---------- 图纸感图框 ---------- */
.figure {
  border: 1.5px solid var(--ink);
  background:
    linear-gradient(var(--grid) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid) 1px, transparent 1px),
    #fdfdfb;
  background-size: 24px 24px, 24px 24px, auto;
  padding: 28px 24px 18px;
  margin: 28px 0;
}
.figure svg { display: block; width: 100%; height: auto; }
.figcap {
  font-family: var(--mono);
  font-size: 12px;
  color: var(--muted);
  letter-spacing: 0.08em;
  margin-top: 14px;
  border-top: 1px dashed var(--line);
  padding-top: 10px;
}
.figcap b { color: var(--blue); font-weight: 700; }

/* ---------- 卡片 ---------- */
.grid { display: grid; gap: 20px; }
.grid.cols-2 { grid-template-columns: repeat(2, 1fr); }
.grid.cols-3 { grid-template-columns: repeat(3, 1fr); }
@media (max-width: 860px) {
  .grid.cols-2, .grid.cols-3 { grid-template-columns: 1fr; }
}

.card {
  border: 1.5px solid var(--ink);
  background: #fff;
  padding: 24px;
  position: relative;
  box-shadow: 4px 4px 0 var(--blue-wash);
}
.card h3 { margin-top: 0; }
.card .tag {
  display: inline-block;
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.12em;
  color: var(--paper);
  background: var(--blue);
  padding: 2px 8px;
  margin-bottom: 12px;
}
.card .tag.red { background: var(--red); }
.card p { font-size: 15px; color: #3a3f46; }
a.card { display: block; text-decoration: none; color: inherit; transition: transform 0.15s ease, box-shadow 0.15s ease; }
a.card:hover { transform: translate(-2px, -2px); box-shadow: 7px 7px 0 var(--blue-wash); }

/* ---------- 时间线 ---------- */
.timeline { position: relative; margin: 36px 0; padding-left: 34px; }
.timeline::before {
  content: "";
  position: absolute;
  left: 8px; top: 6px; bottom: 6px;
  width: 2px;
  background: var(--blue);
}
.t-item { position: relative; padding: 0 0 34px; }
.t-item::before {
  content: "";
  position: absolute;
  left: -32px; top: 8px;
  width: 12px; height: 12px;
  background: var(--paper);
  border: 3px solid var(--blue);
  border-radius: 50%;
}
.t-item.milestone::before { background: var(--red); border-color: var(--red); }
.t-year {
  font-family: var(--mono);
  font-weight: 700;
  font-size: 15px;
  color: var(--blue-deep);
  letter-spacing: 0.06em;
}
.t-item h3 { margin: 4px 0 6px; font-size: 18px; }
.t-item p { margin: 0; font-size: 15px; color: #3a3f46; max-width: 640px; }

/* ---------- 章节精读块 ---------- */
.chapter {
  border-left: 4px solid var(--blue);
  padding: 8px 0 8px 26px;
  margin: 44px 0;
}
.chapter .ch-no {
  font-family: var(--mono);
  font-size: 12px;
  letter-spacing: 0.2em;
  color: var(--blue);
}
.chapter h3 { margin-top: 6px; font-size: 24px; }
.chapter ul { margin: 12px 0 12px 22px; }
.chapter li { margin: 8px 0; font-size: 15.5px; }
.keybox {
  background: var(--paper-deep);
  border: 1px solid var(--line);
  padding: 14px 18px;
  margin: 16px 0;
  font-size: 15px;
}
.keybox b { font-family: var(--mono); font-size: 12px; letter-spacing: 0.15em; color: var(--red); display: block; margin-bottom: 6px; }

/* 难度标记 */
.difficulty {
  display: inline-flex;
  gap: 3px;
  vertical-align: middle;
  margin-left: 10px;
}
.difficulty i {
  width: 9px; height: 9px;
  border: 1.5px solid var(--blue);
  border-radius: 50%;
  display: inline-block;
}
.difficulty i.on { background: var(--blue); }
.difficulty.hard i { border-color: var(--red); }
.difficulty.hard i.on { background: var(--red); }

/* ---------- 首页 Hero ---------- */
.hero {
  padding: 84px 0 64px;
  border-bottom: 2px solid var(--ink);
  background:
    linear-gradient(var(--grid) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid) 1px, transparent 1px),
    var(--paper);
  background-size: 32px 32px;
}
.hero-grid {
  display: grid;
  grid-template-columns: 1.1fr 1fr;
  gap: 48px;
  align-items: center;
}
@media (max-width: 860px) { .hero-grid { grid-template-columns: 1fr; } }
.hero .lede { margin-top: 20px; }

/* 反馈回路动画：信号沿闭环流动 */
.loop-flow {
  stroke-dasharray: 10 8;
  animation: loopflow 1.6s linear infinite;
}
@keyframes loopflow {
  to { stroke-dashoffset: -18; }
}

/* ---------- 交互模拟器 ---------- */
.sim {
  border: 2px solid var(--ink);
  background: #fff;
  padding: 26px;
  margin: 30px 0;
  box-shadow: 6px 6px 0 var(--blue-wash);
}
.sim-title { font-family: var(--mono); font-size: 13px; letter-spacing: 0.16em; color: var(--blue); margin-bottom: 16px; }
.sim-canvas {
  height: 180px;
  border: 1px solid var(--line);
  background:
    linear-gradient(var(--grid) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid) 1px, transparent 1px),
    #fdfdfb;
  background-size: 20px 20px;
  position: relative;
  overflow: hidden;
}
.sim-controls { display: flex; flex-wrap: wrap; gap: 20px 36px; margin-top: 18px; align-items: center; }
.sim-controls label { font-family: var(--mono); font-size: 12px; letter-spacing: 0.1em; color: var(--muted); display: flex; align-items: center; gap: 10px; }
.sim-controls input[type="range"] { accent-color: var(--blue); width: 140px; }
.sim-controls button {
  font-family: var(--mono);
  font-size: 12px;
  letter-spacing: 0.1em;
  background: var(--red);
  color: #fff;
  border: none;
  padding: 9px 16px;
  cursor: pointer;
}
.sim-controls button:hover { background: #a02f22; }
.sim-readout { font-family: var(--mono); font-size: 13px; color: var(--blue-deep); font-weight: 700; }

/* ---------- 页脚 ---------- */
footer {
  border-top: 2px solid var(--ink);
  margin-top: 40px;
  padding: 36px 0 48px;
  background: var(--paper-deep);
}
footer .wrap { display: flex; flex-wrap: wrap; gap: 12px 32px; justify-content: space-between; align-items: baseline; }
footer p, footer a { font-family: var(--mono); font-size: 12px; color: var(--muted); letter-spacing: 0.06em; }
footer a { text-decoration: none; }
footer a:hover { color: var(--blue); }

/* ---------- 页面页眉 ---------- */
.page-head { padding: 64px 0 48px; border-bottom: 2px solid var(--ink); }
.page-head .lede { margin-top: 16px; }

/* ---------- 概念条目 ---------- */
.concept { margin: 56px 0; }
.concept .prose { margin-bottom: 6px; }

/* 术语对照表 */
table.terms { width: 100%; border-collapse: collapse; margin: 24px 0; font-size: 15px; }
table.terms th, table.terms td { border: 1px solid var(--line); padding: 10px 14px; text-align: left; }
table.terms th { background: var(--blue-wash); font-family: var(--mono); font-size: 12px; letter-spacing: 0.12em; color: var(--blue-deep); }
table.terms td:first-child { font-weight: 700; white-space: nowrap; }

:focus-visible { outline: 3px solid var(--red); outline-offset: 2px; }