/* === Shared Course Stylesheet (v2, 2026-10-17) === */
/* Clean, Tufte-inspired typography for the CS self-study course. */

:root {
  --font-body: 'Segoe UI', system-ui, -apple-system, 'PingFang SC', 'Microsoft YaHei', sans-serif;
  --font-mono: 'Cascadia Code', 'Fira Code', 'Consolas', 'Courier New', monospace;
  --font-heading: 'Segoe UI', system-ui, -apple-system, 'PingFang SC', 'Microsoft YaHei', sans-serif;
  --color-bg: #fffff8;
  --color-text: #111;
  --color-muted: #555;
  --color-accent: #2563eb;
  --color-accent-soft: #eef2ff;
  --color-border: #ddd;
  --color-code-bg: #f4f4f4;
  --color-success: #166534;
  --color-success-bg: #dcfce7;
  --color-error: #991b1b;
  --color-error-bg: #fee2e2;
  --color-warn-bg: #fef9c3;
  --max-width: 720px;
  --shadow-soft: 0 1px 2px rgba(0, 0, 0, 0.04);
}

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

body {
  font-family: var(--font-body);
  font-size: 17px;
  line-height: 1.7;
  color: var(--color-text);
  background: var(--color-bg);
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 2.5rem 1.5rem 5rem;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

/* 标题 */
h1 {
  font-family: var(--font-heading);
  font-size: clamp(1.6rem, 4vw, 2rem);
  font-weight: 700;
  line-height: 1.3;
  letter-spacing: -0.01em;
  margin: 0 0 0.5rem;
}

h2 {
  font-family: var(--font-heading);
  font-size: 1.32rem;
  font-weight: 600;
  line-height: 1.4;
  margin: 2.4rem 0 0.6rem;
  padding-bottom: 0.3rem;
  border-bottom: 1px solid var(--color-border);
  color: var(--color-accent);
  scroll-margin-top: 1rem;
}

h3 {
  font-family: var(--font-heading);
  font-size: 1.08rem;
  font-weight: 600;
  margin: 1.6rem 0 0.4rem;
}

/* 标题下的一句副标题 */
.lede,
h1 + p em,
p > em:only-child {
  color: var(--color-muted);
}

p { margin: 0.6rem 0; }

a { color: var(--color-accent); text-decoration: none; }
a:hover { text-decoration: underline; }
a:focus-visible { outline: 2px solid var(--color-accent); outline-offset: 2px; border-radius: 2px; }

ul, ol { padding-left: 1.5rem; margin: 0.6rem 0; }
li { margin: 0.3rem 0; }
li > ul, li > ol { margin: 0.3rem 0; }

strong { font-weight: 650; }
hr { border: 0; border-top: 1px solid var(--color-border); margin: 2rem 0; }

/* 代码 */
pre {
  background: var(--color-code-bg);
  border: 1px solid var(--color-border);
  border-radius: 8px;
  padding: 1rem 1.15rem;
  overflow-x: auto;
  font-family: var(--font-mono);
  font-size: 13.5px;
  line-height: 1.6;
  margin: 1rem 0;
  tab-size: 2;
  box-shadow: var(--shadow-soft);
}

code {
  font-family: var(--font-mono);
  font-size: 0.88em;
  background: #f1f3f5;
  padding: 0.12em 0.35em;
  border-radius: 4px;
}

pre code {
  background: transparent;
  padding: 0;
  border-radius: 0;
  font-size: inherit;
}

/* 提示框 */
.callout {
  border-left: 4px solid var(--color-accent);
  padding: 0.7rem 1rem;
  margin: 1.1rem 0;
  background: #f0f4ff;
  border-radius: 0 6px 6px 0;
  font-size: 0.96em;
}

.callout--warn {
  border-left-color: #ca8a04;
  background: var(--color-warn-bg);
}

/* 关键结论框 */
.keypoint {
  border: 1px solid var(--color-border);
  border-left: 4px solid var(--color-success);
  background: #f6fdf9;
  padding: 0.75rem 1rem;
  border-radius: 0 6px 6px 0;
  margin: 1.1rem 0;
  font-size: 0.96em;
  box-shadow: var(--shadow-soft);
}

.keypoint > strong:first-child { color: var(--color-success); }

/* 本课速览（页首那张小卡片） */
nav.toc {
  border: 1px solid var(--color-border);
  border-radius: 8px;
  padding: 0.8rem 1.1rem;
  margin: 1.2rem 0 1.8rem;
  background: #fcfcfa;
  font-size: 0.92em;
}

nav.toc > strong { display: block; margin-bottom: 0.3rem; color: var(--color-muted); font-size: 0.9em; letter-spacing: 0.04em; }
nav.toc ol { margin: 0.2rem 0; padding-left: 1.3rem; }
nav.toc li { margin: 0.15rem 0; }
nav.toc a { color: var(--color-text); }
nav.toc a:hover { color: var(--color-accent); }

/* 逐轮推演表 / 普通表 */
table {
  border-collapse: collapse;
  width: 100%;
  margin: 1.1rem 0;
  font-size: 0.94em;
  box-shadow: var(--shadow-soft);
}

th, td {
  border: 1px solid var(--color-border);
  padding: 0.45rem 0.7rem;
  text-align: left;
  vertical-align: top;
}

thead th { background: #f3f4f6; font-weight: 650; }
th { background: #fafafa; font-weight: 600; }
tbody tr:nth-child(even) td { background: #fcfcf9; }
td code { font-size: 0.85em; }

/* 编号步骤（.steps > li） */
.steps { counter-reset: step; list-style: none; padding-left: 0; margin: 0.9rem 0; }
.steps > li { counter-increment: step; position: relative; padding-left: 2.3rem; margin: 0.6rem 0; }
.steps > li::before {
  content: counter(step);
  position: absolute; left: 0; top: 0.1rem;
  width: 1.55rem; height: 1.55rem; line-height: 1.55rem;
  text-align: center; border-radius: 50%;
  background: var(--color-accent); color: #fff;
  font-size: 0.8em; font-weight: 600;
}

/* 逐轮推演表 */
table.trace { font-family: var(--font-mono); font-size: 0.85em; }
table.trace th { font-family: var(--font-body); font-size: 0.95em; }
table.trace td { padding: 0.35rem 0.6rem; white-space: nowrap; }
table.trace tr.stamp td { background: #eef4ff; }
table.trace tr.stamp td:first-child { border-left: 3px solid var(--color-accent); }

/* 行内小标签 */
.chip {
  display: inline-block;
  padding: 0.05rem 0.45rem;
  border-radius: 999px;
  background: var(--color-accent-soft);
  color: var(--color-accent);
  font-family: var(--font-mono);
  font-size: 0.8em;
}

.muted { color: var(--color-muted); font-size: 0.9em; }

/* 小测 */
.quiz { margin: 1.6rem 0; }
.quiz__question { font-weight: 650; margin-bottom: 0.55rem; line-height: 1.5; }
.quiz__options { display: flex; flex-direction: column; gap: 0.4rem; }
.quiz__option {
  display: block;
  width: 100%;
  text-align: left;
  padding: 0.55rem 0.85rem;
  border: 1px solid var(--color-border);
  border-radius: 8px;
  cursor: pointer;
  background: #fff;
  color: inherit;
  font-family: inherit;
  font-size: 0.95em;
  line-height: 1.5;
  transition: background 0.15s, border-color 0.15s, transform 0.05s;
}
.quiz__option:hover { background: #f0f4ff; border-color: #c7d2fe; }
.quiz__option:active { transform: scale(0.995); }
.quiz__option:focus-visible { outline: 2px solid var(--color-accent); outline-offset: 2px; }
.quiz__option--selected { background: #dbeafe; border-color: var(--color-accent); }
.quiz__option--correct { background: var(--color-success-bg); border-color: #22c55e; color: var(--color-success); }
.quiz__option--wrong { background: var(--color-error-bg); border-color: #ef4444; color: var(--color-error); }
.quiz__feedback { margin-top: 0.6rem; padding: 0.6rem 0.85rem; border-radius: 6px; display: none; }
.quiz__feedback--show { display: block; }
.quiz__feedback--correct { background: var(--color-success-bg); color: var(--color-success); }
.quiz__feedback--wrong { background: var(--color-error-bg); color: var(--color-error); }

/* 页尾 */
.lesson-meta {
  color: var(--color-muted);
  font-size: 0.85em;
  line-height: 1.75;
  margin-top: 3rem;
  padding-top: 1rem;
  border-top: 1px solid var(--color-border);
}

.lesson-meta a { color: var(--color-muted); }
.lesson-meta p { margin: 0.3rem 0; }

.footer-nav {
  margin-top: 2rem;
  padding-top: 1rem;
  border-top: 1px solid var(--color-border);
  display: flex;
  flex-wrap: wrap;
  gap: 0.6rem 1.2rem;
  justify-content: space-between;
  align-items: baseline;
  font-size: 0.95em;
}
.footer-nav a { font-weight: 500; }
.footer-nav span { color: var(--color-muted); }

/* 标签 */
.tag {
  display: inline-block;
  font-size: 0.75em;
  padding: 0.05rem 0.45rem;
  border-radius: 4px;
  background: var(--color-accent-soft);
  color: var(--color-accent);
  margin-right: 0.3rem;
  vertical-align: 0.05em;
}
.tag-book { background: #fff7ed; color: #9a3412; }
.t-b { background: #f0fdf4; color: #166534; }

/* 窄屏 */
@media (max-width: 600px) {
  body { font-size: 16px; padding: 1.5rem 1rem 3.5rem; }
  h2 { font-size: 1.2rem; }
  pre { font-size: 12.5px; padding: 0.8rem; }
  table { font-size: 0.85em; }
  .footer-nav { flex-direction: column; align-items: flex-start; }
}

@media print {
  body { font-size: 11pt; padding: 0; max-width: none; }
  pre { font-size: 9.5pt; box-shadow: none; page-break-inside: avoid; }
  table { page-break-inside: avoid; box-shadow: none; }
  .footer-nav, nav.toc { display: none; }
  a { color: inherit; text-decoration: none; }
}