/* ============================================================
   系统设计课程 · 共享样式表
   所有 lessons/ 与 reference/ 文档统一链接此文件。
   设计基调：纸质、衬线标题、克制配色、适合打印。
   ============================================================ */

:root {
  --paper: #faf8f4;
  --card: #ffffff;
  --ink: #1c1b18;
  --muted: #6f6a60;
  --border: #e5e1d8;
  --accent: #0e5a8a;
  --accent-soft: #e6eff6;
  --good: #1a7f4e;
  --good-soft: #e6f4ec;
  --bad: #b3372e;
  --bad-soft: #faeae8;
  --warn: #8a6a1a;
  --warn-soft: #f8f1dc;
  --serif: "Iowan Old Style", "Palatino Linotype", "Palatino", "Songti SC", "Noto Serif SC", serif;
  --sans: "PingFang SC", "Helvetica Neue", "Noto Sans SC", "Microsoft YaHei", sans-serif;
  --mono: "SF Mono", "JetBrains Mono", Menlo, Consolas, monospace;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 17px;
  line-height: 1.9;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

main {
  max-width: 780px;
  margin: 0 auto;
  padding: 56px 28px 110px;
}

/* ---------- 课程头部 ---------- */
.lesson-kicker {
  font-family: var(--sans);
  font-size: 12.5px;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--accent);
  margin-bottom: 14px;
}

.lesson-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 8px 18px;
  color: var(--muted);
  font-size: 14px;
  margin: 18px 0 8px;
}

h1 {
  font-family: var(--serif);
  font-size: 40px;
  line-height: 1.25;
  font-weight: 700;
  margin: 0 0 6px;
  letter-spacing: 0.01em;
}

h2 {
  font-family: var(--serif);
  font-size: 26px;
  line-height: 1.35;
  margin: 64px 0 18px;
  padding-top: 10px;
}

h2 .sec-no {
  color: var(--accent);
  font-size: 15px;
  font-family: var(--sans);
  font-weight: 600;
  letter-spacing: 0.14em;
  display: block;
  margin-bottom: 4px;
}

h3 {
  font-family: var(--serif);
  font-size: 20px;
  margin: 36px 0 10px;
}

p { margin: 0 0 18px; }

a { color: var(--accent); text-decoration-thickness: 1px; text-underline-offset: 3px; }
a:hover { text-decoration-thickness: 2px; }

strong { font-weight: 650; }

/* 英文术语标注 */
.term {
  font-family: var(--sans);
  font-size: 0.82em;
  color: var(--muted);
  border-bottom: 1px dotted var(--border);
  white-space: nowrap;
}

/* ---------- 卡片与区块 ---------- */
.callout {
  background: var(--card);
  border: 1px solid var(--border);
  border-left: 4px solid var(--accent);
  border-radius: 8px;
  padding: 18px 22px;
  margin: 26px 0;
}
.callout.mission { border-left-color: var(--accent); background: var(--accent-soft); }
.callout.tip { border-left-color: var(--good); }
.callout.warn { border-left-color: var(--warn); }
.callout.danger { border-left-color: var(--bad); }
.callout .callout-title {
  font-weight: 650;
  font-size: 13px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 6px;
}
.callout p:last-child { margin-bottom: 0; }

.step-card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 22px 26px 16px;
  margin: 26px 0;
}
.step-card .step-badge {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 30px; height: 30px;
  border-radius: 50%;
  background: var(--accent);
  color: #fff;
  font-weight: 700;
  font-size: 15px;
  margin-right: 10px;
  vertical-align: middle;
}
.step-card h3 { display: inline; margin: 0; }
.step-card .step-output {
  margin-top: 14px;
  padding: 10px 14px;
  background: var(--paper);
  border-radius: 6px;
  font-size: 15px;
}
.step-card .step-output strong { color: var(--accent); }

/* ---------- 表格 ---------- */
table {
  width: 100%;
  border-collapse: collapse;
  margin: 22px 0;
  font-size: 15.5px;
  background: var(--card);
}
th, td {
  border: 1px solid var(--border);
  padding: 9px 14px;
  text-align: left;
  vertical-align: top;
}
th {
  background: var(--paper);
  font-weight: 650;
  font-size: 14px;
  letter-spacing: 0.04em;
}

/* ---------- 代码 ---------- */
code {
  font-family: var(--mono);
  font-size: 0.86em;
  background: #f0ede6;
  border-radius: 4px;
  padding: 1.5px 6px;
}
pre {
  background: #26221b;
  color: #f2efe8;
  border-radius: 8px;
  padding: 18px 22px;
  overflow-x: auto;
  font-size: 14px;
  line-height: 1.7;
}
pre code { background: none; color: inherit; padding: 0; }

blockquote {
  margin: 26px 0;
  padding: 4px 24px;
  border-left: 3px solid var(--accent);
  color: var(--muted);
  font-style: italic;
}
blockquote cite { display: block; margin-top: 8px; font-size: 14px; font-style: normal; }

/* ---------- 上标引用 ---------- */
sup.cite a {
  text-decoration: none;
  font-size: 0.72em;
  color: var(--accent);
  padding: 0 2px;
}

/* ---------- 检索练习 ---------- */
.retrieval {
  background: var(--card);
  border: 1.5px dashed var(--accent);
  border-radius: 10px;
  padding: 22px 26px;
  margin: 30px 0;
}
.retrieval textarea {
  width: 100%;
  min-height: 130px;
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 12px 14px;
  font-family: var(--sans);
  font-size: 15px;
  line-height: 1.8;
  background: var(--paper);
  resize: vertical;
}

details {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 12px 20px;
  margin: 18px 0;
}
details summary {
  cursor: pointer;
  font-weight: 600;
  color: var(--accent);
}
details[open] summary { margin-bottom: 10px; }

/* ---------- 课程页脚导航 ---------- */
.lesson-footer {
  margin-top: 80px;
  padding-top: 26px;
  border-top: 2px solid var(--border);
  display: flex;
  justify-content: space-between;
  gap: 16px;
  font-size: 15px;
}
.lesson-footer .next { text-align: right; }

.ask-teacher {
  margin-top: 40px;
  text-align: center;
  background: var(--accent-soft);
  border-radius: 10px;
  padding: 18px 26px;
  font-size: 15.5px;
}

/* ---------- 打印 ---------- */
@media print {
  body { background: #fff; font-size: 12.5pt; }
  main { max-width: none; padding: 0; }
  .step-card, .callout, table, .retrieval, details { break-inside: avoid; }
  h2 { break-after: avoid; }
  .ask-teacher, .lesson-footer { display: none; }
  a { color: var(--ink); text-decoration: none; }
  details { border: none; padding: 0; }
  details summary { display: none; }
}