/* ============================================================
   第2章 使用 matplotlib 绘制简单图表 · 小清新主题
   ============================================================ */

:root {
  --bg: #F6FAF8;
  --bg-soft: #FBFDFC;
  --card: #FFFFFF;
  --ink: #2B463F;
  --ink-2: #4E6C64;
  --muted: #8AA49D;
  --line: #E4EFEB;
  --line-2: #EFF5F2;

  --teal: #5FB49C;
  --mint: #A8D8C9;
  --mint-l: #DCEFE8;
  --coral: #F2A28C;
  --coral-l: #FDEDE7;
  --sand: #F3CE8E;
  --blue: #9BC1DC;
  --lilac: #C3B3DD;
  --sage: #BFD8A5;

  --serif: "Songti SC", "STSong", "SimSun", Georgia, "Times New Roman", serif;
  --sans: -apple-system, BlinkMacSystemFont, "PingFang SC", "Hiragino Sans GB",
          "Microsoft YaHei", "Helvetica Neue", Arial, sans-serif;
  --mono: "SF Mono", "JetBrains Mono", Menlo, Consolas, "Courier New", monospace;

  --shadow: 0 10px 30px rgba(95, 180, 156, 0.08);
  --radius: 18px;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 16px;
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
  letter-spacing: .01em;
}

/* ---------- 顶部进度条 ---------- */
.progress {
  position: fixed;
  top: 0; left: 0; right: 0;
  height: 3px;
  background: transparent;
  z-index: 100;
}
.progress i {
  display: block;
  height: 100%;
  width: 0;
  background: linear-gradient(90deg, var(--mint), var(--teal), var(--coral));
  border-radius: 0 3px 3px 0;
  transition: width .1s linear;
}

/* ---------- 导航 ---------- */
.nav {
  position: sticky;
  top: 0;
  z-index: 60;
  background: rgba(246, 250, 248, .82);
  backdrop-filter: saturate(180%) blur(14px);
  -webkit-backdrop-filter: saturate(180%) blur(14px);
  border-bottom: 1px solid var(--line-2);
}
.nav-inner {
  max-width: 1180px;
  margin: 0 auto;
  padding: 0 28px;
  height: 56px;
  display: flex;
  align-items: center;
  gap: 26px;
}
.nav-brand {
  display: flex;
  align-items: baseline;
  gap: 8px;
  text-decoration: none;
  color: var(--ink);
  flex-shrink: 0;
}
.nav-brand em {
  font-family: var(--mono);
  font-style: normal;
  font-size: 14px;
  font-weight: 600;
  color: var(--teal);
  letter-spacing: .02em;
}
.nav-brand span { font-size: 12px; color: var(--muted); }

.nav-links {
  display: flex;
  gap: 4px;
  overflow-x: auto;
  scrollbar-width: none;
  padding: 4px 0;
}
.nav-links::-webkit-scrollbar { display: none; }
.nav-links a {
  flex-shrink: 0;
  padding: 5px 11px;
  border-radius: 999px;
  font-size: 13px;
  color: var(--ink-2);
  text-decoration: none;
  white-space: nowrap;
  transition: background .2s, color .2s;
}
.nav-links a:hover { background: var(--mint-l); color: var(--ink); }
.nav-links a.on {
  background: var(--teal);
  color: #fff;
  box-shadow: 0 4px 12px rgba(95, 180, 156, .28);
}

/* ---------- Hero ---------- */
.hero {
  position: relative;
  overflow: hidden;
  padding: 96px 28px 84px;
  background:
    radial-gradient(900px 420px at 12% -10%, #EAF6F1 0%, rgba(234,246,241,0) 70%),
    radial-gradient(700px 360px at 92% 8%, #FDF1EC 0%, rgba(253,241,236,0) 68%),
    linear-gradient(180deg, #F9FCFA 0%, var(--bg) 100%);
  border-bottom: 1px solid var(--line-2);
}
.hero-inner {
  position: relative;
  z-index: 2;
  max-width: 980px;
  margin: 0 auto;
}
.hero-orb {
  position: absolute;
  border-radius: 50%;
  filter: blur(2px);
  opacity: .5;
  pointer-events: none;
}
.orb-a {
  width: 260px; height: 260px;
  right: -70px; top: 40px;
  background: radial-gradient(circle at 35% 30%, #CBEADF, #EAF6F1);
}
.orb-b {
  width: 170px; height: 170px;
  right: 130px; bottom: -50px;
  background: radial-gradient(circle at 40% 30%, #FBDCD0, #FDF1EC);
}
.orb-c {
  width: 120px; height: 120px;
  left: -40px; bottom: 40px;
  background: radial-gradient(circle at 40% 30%, #FFF0D8, #FCF7EC);
}

.eyebrow {
  margin: 0 0 22px;
  font-family: var(--mono);
  font-size: 12.5px;
  letter-spacing: .14em;
  color: var(--teal);
  text-transform: uppercase;
}
.hero h1 {
  margin: 0 0 26px;
  font-family: var(--serif);
  font-weight: 600;
  font-size: clamp(38px, 6vw, 66px);
  line-height: 1.22;
  letter-spacing: .02em;
  color: #25403A;
}
.hero h1 span {
  background: linear-gradient(100deg, #4FA78F 10%, #79C0AC 55%, #8FB9D6 95%);
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}
.lede {
  max-width: 680px;
  margin: 0 0 34px;
  font-size: 16.5px;
  line-height: 1.9;
  color: var(--ink-2);
}
.hero-tags {
  display: flex;
  flex-wrap: wrap;
  gap: 9px;
  margin: 0 0 42px;
  padding: 0;
  list-style: none;
}
.hero-tags li {
  padding: 6px 14px;
  border-radius: 999px;
  background: #fff;
  border: 1px solid var(--line);
  font-size: 13px;
  color: var(--ink-2);
  box-shadow: 0 2px 8px rgba(95, 180, 156, .05);
}
.hero-tags li:nth-child(3n+1) { border-color: #CDE7DE; }
.hero-tags li:nth-child(3n+2) { border-color: #F7DDD3; }
.hero-tags li:nth-child(3n+3) { border-color: #EDE4F5; }

.hero-stats {
  display: flex;
  gap: 56px;
  padding-top: 30px;
  border-top: 1px solid var(--line);
  flex-wrap: wrap;
}
.hero-stats div { display: flex; align-items: baseline; gap: 10px; }
.hero-stats b {
  font-family: var(--serif);
  font-size: 34px;
  font-weight: 600;
  color: var(--teal);
  line-height: 1;
}
.hero-stats span { font-size: 13px; color: var(--muted); }

/* ---------- 通用区块 ---------- */
main { display: block; }

.sec {
  max-width: 1120px;
  margin: 0 auto;
  padding: 88px 28px 24px;
}
.sec-tight { padding-top: 76px; }

.kicker {
  margin: 0 0 10px;
  font-family: var(--mono);
  font-size: 11.5px;
  letter-spacing: .16em;
  text-transform: uppercase;
  color: var(--mint);
}

.sec-head {
  display: flex;
  align-items: flex-start;
  gap: 22px;
  margin-bottom: 34px;
  padding-bottom: 26px;
  border-bottom: 1px solid var(--line);
}
.sec-head > div { flex: 1; }
.sec-num {
  font-family: var(--serif);
  font-size: 46px;
  font-weight: 600;
  line-height: 1;
  color: #CFE6DE;
  letter-spacing: -.02em;
  padding-top: 4px;
  min-width: 84px;
}
.sec-title {
  margin: 0 0 8px;
  font-family: var(--serif);
  font-size: clamp(25px, 3.2vw, 32px);
  font-weight: 600;
  letter-spacing: .02em;
  color: #25403A;
}
.sec-sub {
  margin: 0;
  font-size: 14.5px;
  color: var(--muted);
  line-height: 1.8;
}
.sec-head-block { display: block; }
.sec-head-block .sec-title { margin-bottom: 10px; }
.sec-head-block .sec-sub { max-width: 720px; }

h3.sub {
  display: flex;
  align-items: center;
  gap: 12px;
  margin: 54px 0 18px;
  font-size: 20px;
  font-weight: 600;
  letter-spacing: .01em;
  color: #2A463F;
}
.sub-id {
  font-family: var(--mono);
  font-size: 12px;
  font-weight: 600;
  color: var(--teal);
  background: #EAF6F1;
  border-radius: 6px;
  padding: 3px 8px;
  letter-spacing: .02em;
}

.lead-text {
  margin: 0 0 18px;
  font-size: 15.5px;
  color: var(--ink-2);
}

code.ic {
  font-family: var(--mono);
  font-size: .88em;
  background: #EEF7F3;
  color: #3D8874;
  border-radius: 5px;
  padding: 1px 6px;
  white-space: nowrap;
}

/* ---------- 卡片 ---------- */
.card {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 26px 28px;
  box-shadow: var(--shadow);
  margin-bottom: 22px;
}
.card-flat { padding: 20px 22px; margin: 0; box-shadow: none; }
.card-t {
  margin: 0 0 14px;
  font-family: var(--mono);
  font-size: 11.5px;
  letter-spacing: .14em;
  text-transform: uppercase;
  color: var(--teal);
}

.sig {
  margin: 0 0 20px;
  padding: 16px 18px;
  background: #F4FAF7;
  border-left: 3px solid var(--mint);
  border-radius: 0 12px 12px 0;
  font-family: var(--mono);
  font-size: 13px;
  line-height: 1.85;
  color: #3B6E60;
  white-space: pre-wrap;
  word-break: break-word;
  overflow-x: auto;
}

.params { margin: 0; }
.params > div {
  display: grid;
  grid-template-columns: 110px 1fr;
  gap: 16px;
  padding: 9px 0;
  border-top: 1px dashed var(--line-2);
}
.params > div:first-child { border-top: none; }
.params dt {
  font-family: var(--mono);
  font-size: 13px;
  font-weight: 600;
  color: #3D8874;
}
.params dd {
  margin: 0;
  font-size: 14.5px;
  color: var(--ink-2);
  line-height: 1.8;
}

.note {
  margin: 18px 0 0;
  padding: 13px 16px;
  background: #FBF7EF;
  border: 1px solid #F5EAD6;
  border-radius: 12px;
  font-size: 14px;
  color: #7A6A4C;
  line-height: 1.85;
}

.grid-3 {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 18px;
  margin-bottom: 8px;
}

/* ---------- 代码 ---------- */
pre.code {
  margin: 0;
  padding: 16px 18px;
  background: #F5FAF8;
  border: 1px solid var(--line);
  border-radius: 12px;
  font-family: var(--mono);
  font-size: 12.5px;
  line-height: 1.85;
  color: #3A5850;
  overflow-x: auto;
  white-space: pre;
}
pre.code .cm { color: #93B3A9; font-style: italic; }

/* ---------- 示例网格 ---------- */
.demo-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 22px;
  margin-top: 26px;
}
.demo {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 22px 22px 18px;
  box-shadow: var(--shadow);
}
.demo-wide { margin-top: 26px; }
.demo-t {
  margin: 0 0 6px;
  font-size: 15px;
  font-weight: 600;
  color: #2A463F;
  letter-spacing: .01em;
}
.demo-d {
  margin: 0 0 12px;
  font-size: 13.5px;
  color: var(--muted);
  line-height: 1.8;
}
.two-col {
  display: grid;
  grid-template-columns: 1fr;
  gap: 14px;
  margin-top: 12px;
}
.two-col-wide {
  grid-template-columns: 1.05fr 1fr;
  align-items: center;
}

/* ---------- 图表 ---------- */
.chart {
  width: 100%;
  height: 340px;
}
.chart.sm { height: 240px; }
.chart.tall { height: 470px; }

.chart-wrap { min-width: 0; }
.chart-cap {
  margin: 12px 0 0;
  font-size: 12.5px;
  color: var(--muted);
  line-height: 1.75;
  text-align: center;
}

/* ---------- 案例 ---------- */
.case {
  margin-top: 26px;
  padding: 30px;
  background: linear-gradient(180deg, #FFFFFF 0%, #FDFFFE 100%);
  border: 1px solid var(--line);
  border-radius: 22px;
  box-shadow: 0 14px 40px rgba(95, 180, 156, .09);
}
.case-head {
  display: flex;
  align-items: center;
  gap: 14px;
  margin-bottom: 16px;
  flex-wrap: wrap;
}
.case-head h4 {
  margin: 0;
  font-family: var(--serif);
  font-size: 21px;
  font-weight: 600;
  letter-spacing: .02em;
  color: #25403A;
}
.case-tag {
  font-family: var(--mono);
  font-size: 11.5px;
  letter-spacing: .06em;
  color: #C97A5F;
  background: var(--coral-l);
  border: 1px solid #F8DCD2;
  border-radius: 999px;
  padding: 3px 11px;
  white-space: nowrap;
}
.case-desc {
  margin: 0 0 24px;
  font-size: 15px;
  line-height: 1.95;
  color: var(--ink-2);
}
.case-grid {
  display: grid;
  grid-template-columns: 1fr 1.1fr;
  gap: 30px;
  align-items: start;
}
.case-grid-wide { grid-template-columns: 1fr 1.15fr; }

/* ---------- 表格 ---------- */
.table-wrap { min-width: 0; }
.tbl-cap {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  gap: 12px;
  margin: 0 0 12px;
  font-size: 13.5px;
  font-weight: 600;
  color: #3F5F57;
}
.tbl-cap span {
  font-weight: 400;
  font-size: 12px;
  color: var(--muted);
  white-space: nowrap;
}
.tbl {
  width: 100%;
  border-collapse: collapse;
  font-size: 14px;
  font-variant-numeric: tabular-nums;
  background: #fff;
  border-radius: 12px;
  overflow: hidden;
  border: 1px solid var(--line);
}
.tbl th {
  background: #EEF7F3;
  color: #356053;
  font-weight: 600;
  font-size: 13px;
  padding: 11px 10px;
  text-align: center;
  border-bottom: 1px solid #DCEBE5;
  letter-spacing: .02em;
}
.tbl td {
  padding: 9px 10px;
  text-align: center;
  color: var(--ink-2);
  border-bottom: 1px solid var(--line-2);
}
.tbl tbody tr:nth-child(even) { background: #FAFDFB; }
.tbl tbody tr:last-child td { border-bottom: none; }
.tbl tbody tr:hover { background: #F2FAF6; }
.tbl-sm { font-size: 13px; }
.tbl-sm td { padding: 7px 9px; }
.tbl-dense { font-size: 12.5px; }
.tbl-dense td, .tbl-dense th { padding: 7px 6px; }
.tbl td.hl { color: #C97A5F; font-weight: 600; background: #FFF8F5; }
.tbl-sum td { font-weight: 600; color: #356053; background: #F4FAF7; border-top: 1px solid var(--line); }
.tbl-note {
  margin: 12px 0 0;
  font-size: 12.5px;
  color: var(--muted);
  line-height: 1.7;
}

/* ---------- 结论 ---------- */
.insight {
  position: relative;
  margin-top: 26px;
  padding: 18px 22px 18px 26px;
  background: #FFF9F5;
  border: 1px solid #F8E4DA;
  border-radius: 14px;
  font-size: 14.5px;
  line-height: 1.9;
  color: #7C5A4C;
}
.insight::before {
  content: "";
  position: absolute;
  left: 0; top: 14px; bottom: 14px;
  width: 3px;
  border-radius: 3px;
  background: linear-gradient(180deg, var(--coral), var(--sand));
}

/* ---------- 学习目标 ---------- */
.goals {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 20px;
}
.goal {
  position: relative;
  padding: 28px 24px 24px;
  background: #fff;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  overflow: hidden;
}
.goal::after {
  content: "";
  position: absolute;
  right: -30px; top: -30px;
  width: 96px; height: 96px;
  border-radius: 50%;
  background: radial-gradient(circle at 40% 40%, #EDF8F4, rgba(237,248,244,0));
}
.goal-no {
  display: inline-block;
  font-family: var(--serif);
  font-size: 30px;
  font-weight: 600;
  color: #D3E9E2;
  line-height: 1;
  margin-bottom: 14px;
}
.goal h3 {
  margin: 0 0 10px;
  font-size: 16px;
  font-weight: 600;
  color: #2A463F;
  letter-spacing: .01em;
}
.goal p {
  margin: 0;
  font-size: 13.5px;
  color: var(--ink-2);
  line-height: 1.85;
}
.goal-fn {
  margin-top: 14px !important;
  font-family: var(--mono);
  font-size: 11.5px !important;
  color: var(--teal) !important;
  letter-spacing: .02em;
}

/* ---------- 目录 ---------- */
.toc {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 10px 26px;
}
.toc-item {
  display: flex;
  align-items: baseline;
  gap: 14px;
  padding: 14px 18px;
  background: #fff;
  border: 1px solid var(--line);
  border-radius: 12px;
  text-decoration: none;
  transition: transform .2s, border-color .2s, box-shadow .2s;
}
.toc-item:hover {
  transform: translateY(-2px);
  border-color: #CDE7DE;
  box-shadow: 0 10px 24px rgba(95, 180, 156, .12);
}
.toc-no {
  font-family: var(--mono);
  font-size: 12.5px;
  font-weight: 600;
  color: var(--teal);
  min-width: 34px;
}
.toc-name {
  flex: 1;
  font-size: 14.5px;
  color: var(--ink);
  letter-spacing: .01em;
}
.toc-meta {
  font-family: var(--mono);
  font-size: 11.5px;
  color: var(--muted);
}

/* ---------- 小结 ---------- */
.sec-summary { padding-bottom: 60px; }
.summary-card {
  padding: 34px 36px;
  background: linear-gradient(140deg, #FFFFFF 0%, #F4FBF8 100%);
  border: 1px solid var(--line);
  border-radius: 22px;
  box-shadow: 0 16px 44px rgba(95, 180, 156, .1);
}
.summary-card > p {
  margin: 0 0 26px;
  font-size: 15.5px;
  line-height: 2.05;
  color: var(--ink-2);
}
.fn-list {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 12px;
  margin: 0;
  padding: 0;
  list-style: none;
}
.fn-list li {
  padding: 12px 14px;
  background: #fff;
  border: 1px solid var(--line);
  border-radius: 10px;
  display: flex;
  flex-direction: column;
  gap: 2px;
}
.fn-list b {
  font-family: var(--mono);
  font-size: 12.5px;
  color: var(--teal);
  font-weight: 600;
}
.fn-list span { font-size: 12px; color: var(--muted); }

/* ---------- 页脚 ---------- */
.foot {
  padding: 46px 28px 60px;
  text-align: center;
  border-top: 1px solid var(--line);
  background: #F9FCFA;
}
.foot p {
  margin: 0 0 8px;
  font-size: 13.5px;
  color: var(--ink-2);
  letter-spacing: .04em;
}
.foot-sub { font-size: 12px !important; color: var(--muted) !important; }

/* ---------- 入场动画 ---------- */
.js .reveal {
  opacity: 0;
  transform: translateY(16px);
}
.js .reveal.in {
  opacity: 1;
  transform: none;
  transition: opacity .7s cubic-bezier(.22,.61,.36,1), transform .7s cubic-bezier(.22,.61,.36,1);
}

/* ---------- 响应式 ---------- */
@media (max-width: 1024px) {
  .goals { grid-template-columns: repeat(2, 1fr); }
  .grid-3 { grid-template-columns: 1fr; }
  .fn-list { grid-template-columns: repeat(3, 1fr); }
  .case-grid, .case-grid-wide { grid-template-columns: 1fr; gap: 24px; }
  .demo-grid { grid-template-columns: 1fr; }
  .two-col-wide { grid-template-columns: 1fr; }
}

@media (max-width: 720px) {
  .sec { padding: 62px 18px 16px; }
  .hero { padding: 66px 20px 56px; }
  .hero-stats { gap: 28px; }
  .sec-num { font-size: 34px; min-width: 62px; }
  .toc { grid-template-columns: 1fr; }
  .toc-meta { display: none; }
  .case { padding: 22px 18px; }
  .card { padding: 20px 18px; }
  .params > div { grid-template-columns: 1fr; gap: 2px; }
  .fn-list { grid-template-columns: repeat(2, 1fr); }
  .summary-card { padding: 24px 20px; }
  .nav-inner { padding: 0 16px; gap: 14px; }
  .chart { height: 300px; }
  .chart.tall { height: 420px; }
}