/* ===========================================
   百里路 · 现代学术风
   配色：米白 / 深炭 / 砖红 / 灰
   字体：黑体 + Georgia（西文）
   =========================================== */

:root {
  --bg:         #fafaf7;       /* 主背景：暖米白 */
  --bg-soft:    #f3f0e8;       /* 次背景 */
  --paper:      #ffffff;       /* 卡片底 */
  --ink:        #1a1a1a;       /* 主文字：深炭 */
  --ink-mid:    #4a4a48;       /* 次级文字 */
  --ink-light:  #8a8a86;       /* 辅助文字 */
  --line:       #e2dfd6;       /* 分隔线 */
  --line-soft:  #efece4;
  --accent:     #b91c1c;       /* 砖红强调 */
  --accent-soft:#fef3c7;       /* 浅米黄高亮 */
  --tag-bg:     #efece4;
  --code-bg:    #f0ede5;
}

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

html, body {
  font-family: "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Heiti SC", "WenQuanYi Micro Hei", sans-serif;
  background: var(--bg);
  color: var(--ink);
  line-height: 1.75;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  font-feature-settings: "kern", "liga";
}

/* ====== 容器：窄行学术阅读宽度 ====== */
.container {
  max-width: 740px;
  margin: 0 auto;
  padding: 64px 28px 96px;
}
.container.wide { max-width: 1080px; }  /* 首页用 */

/* ====== 头部 ====== */
.site-header {
  border-bottom: 1px solid var(--line);
  padding-bottom: 24px;
  margin-bottom: 48px;
}
.site-header .brand {
  display: flex;
  align-items: baseline;
  gap: 16px;
}
.site-header .logo {
  font-size: 26px;
  font-weight: 600;
  letter-spacing: 0.05em;
  color: var(--ink);
}
.site-header .logo-en {
  font-family: Georgia, "Times New Roman", serif;
  font-size: 13px;
  color: var(--ink-light);
  letter-spacing: 0.25em;
  text-transform: uppercase;
}
.site-header .nav {
  margin-left: auto;
  font-size: 13px;
  color: var(--ink-mid);
  letter-spacing: 0.05em;
}

/* ====== 面包屑 ====== */
.breadcrumb {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 13px;
  color: var(--ink-light);
  padding: 12px 0;
  margin-bottom: 32px;
  border-bottom: 1px solid var(--line);
}
.breadcrumb a {
  color: var(--ink-mid);
  text-decoration: none;
  border-bottom: 1px solid transparent;
  transition: border-color 0.2s;
}
.breadcrumb a:hover { border-bottom-color: var(--accent); color: var(--accent); }
.breadcrumb .lesson-no {
  font-family: Georgia, serif;
  letter-spacing: 0.15em;
}

/* ====== Hero：理论卡片头 ====== */
.lesson-hero {
  padding: 32px 0 40px;
  border-bottom: 2px solid var(--ink);
  margin-bottom: 48px;
}
.lesson-hero .lesson-num {
  font-family: Georgia, serif;
  font-size: 12px;
  letter-spacing: 0.3em;
  color: var(--accent);
  text-transform: uppercase;
  margin-bottom: 14px;
}
.lesson-hero .lesson-title {
  font-size: 42px;
  font-weight: 600;
  letter-spacing: 0.02em;
  line-height: 1.2;
  margin-bottom: 8px;
}
.lesson-hero .lesson-title-en {
  font-family: Georgia, "Times New Roman", serif;
  font-size: 19px;
  font-style: italic;
  color: var(--ink-mid);
  margin-bottom: 24px;
}
.lesson-hero .lesson-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 24px 28px;
  font-size: 13px;
  color: var(--ink-mid);
}
.lesson-hero .lesson-meta dt {
  display: inline;
  color: var(--ink-light);
  margin-right: 6px;
  font-size: 12px;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  font-family: Georgia, serif;
}
.lesson-hero .lesson-meta dd {
  display: inline;
  color: var(--ink);
  font-weight: 500;
}
.lesson-hero .lesson-meta-item {
  display: inline-flex;
  align-items: baseline;
  gap: 6px;
}

/* ====== 章节 ====== */
.section {
  margin-bottom: 56px;
}
.section-head {
  display: flex;
  align-items: baseline;
  gap: 18px;
  margin-bottom: 24px;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--line);
}
.section-head .sec-num {
  font-family: Georgia, serif;
  font-size: 14px;
  color: var(--accent);
  letter-spacing: 0.2em;
  font-weight: 500;
}
.section-head .sec-title {
  font-size: 22px;
  font-weight: 600;
  letter-spacing: 0.04em;
}
.section-head .sec-en {
  margin-left: auto;
  font-family: Georgia, serif;
  font-size: 11px;
  color: var(--ink-light);
  letter-spacing: 0.3em;
  text-transform: uppercase;
}

/* ====== 正文段 ====== */
.section p {
  font-size: 16px;
  line-height: 1.85;
  color: var(--ink);
  margin-bottom: 18px;
}
.section p:last-child { margin-bottom: 0; }
.section strong { color: var(--ink); font-weight: 600; }
.section em { color: var(--accent); font-style: normal; font-weight: 500; }

.section ul, .section ol {
  padding-left: 28px;
  margin-bottom: 18px;
}
.section ul li, .section ol li {
  font-size: 15.5px;
  line-height: 1.85;
  margin-bottom: 8px;
  color: var(--ink);
}

/* ====== 原典：经典定理块 ====== */
.theorem {
  background: var(--paper);
  border: 1px solid var(--line);
  border-left: 4px solid var(--accent);
  padding: 28px 32px;
  margin: 24px 0;
  position: relative;
}
.theorem .theorem-label {
  font-family: Georgia, serif;
  font-size: 11px;
  letter-spacing: 0.3em;
  text-transform: uppercase;
  color: var(--accent);
  margin-bottom: 12px;
}
.theorem .theorem-body {
  font-size: 17px;
  line-height: 1.85;
  color: var(--ink);
}
.theorem .theorem-body em {
  font-style: italic;
  color: var(--ink);
  font-weight: 500;
}
.theorem .theorem-cite {
  display: block;
  text-align: right;
  font-family: Georgia, serif;
  font-size: 13px;
  color: var(--ink-light);
  margin-top: 16px;
  font-style: italic;
}

/* ====== 解读卡：后人之论 ====== */
.commentary {
  display: grid;
  gap: 18px;
}
.commentary-card {
  background: var(--paper);
  border: 1px solid var(--line);
  padding: 22px 26px;
}
.commentary-card .comm-author {
  display: flex;
  align-items: baseline;
  gap: 10px;
  margin-bottom: 12px;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--line-soft);
}
.commentary-card .comm-name {
  font-weight: 600;
  font-size: 15px;
  letter-spacing: 0.06em;
  color: var(--ink);
}
.commentary-card .comm-tag {
  font-family: Georgia, serif;
  font-size: 11px;
  color: var(--ink-light);
  letter-spacing: 0.15em;
  text-transform: uppercase;
}
.commentary-card p {
  font-size: 15px;
  line-height: 1.85;
  color: var(--ink);
  margin-bottom: 10px;
}

/* ====== 案例卡 ====== */
.cases {
  display: grid;
  gap: 20px;
}
.case-card {
  background: var(--paper);
  border: 1px solid var(--line);
  padding: 24px 28px;
}
.case-card .case-meta {
  display: flex;
  align-items: baseline;
  gap: 14px;
  margin-bottom: 14px;
}
.case-card .case-num {
  font-family: Georgia, serif;
  font-size: 13px;
  color: var(--accent);
  letter-spacing: 0.15em;
  font-weight: 500;
}
.case-card .case-title {
  font-size: 17px;
  font-weight: 600;
  letter-spacing: 0.02em;
  color: var(--ink);
}
.case-card .case-when {
  margin-left: auto;
  font-family: Georgia, serif;
  font-size: 12px;
  color: var(--ink-light);
  letter-spacing: 0.1em;
}
.case-card p {
  font-size: 15px;
  line-height: 1.85;
  margin-bottom: 10px;
}
.case-card .case-insight {
  background: var(--accent-soft);
  border-left: 3px solid var(--accent);
  padding: 10px 14px;
  margin-top: 12px;
  font-size: 14.5px;
  color: var(--ink);
}

/* ====== 反例 / 限制 ====== */
.critique-list {
  display: grid;
  gap: 12px;
}
.critique-item {
  background: var(--bg-soft);
  border: 1px solid var(--line);
  border-left: 3px solid var(--ink-mid);
  padding: 14px 20px;
  font-size: 15px;
  line-height: 1.8;
}
.critique-item strong {
  color: var(--accent);
  font-weight: 600;
  margin-right: 6px;
}

/* ====== 相关理论网络 ====== */
.connections {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 14px;
}
@media (max-width: 720px) { .connections { grid-template-columns: 1fr; } }

.conn-item {
  background: var(--paper);
  border: 1px solid var(--line);
  padding: 16px 20px;
}
.conn-item .conn-name {
  font-weight: 600;
  font-size: 15px;
  color: var(--ink);
  margin-bottom: 4px;
}
.conn-item .conn-name-en {
  font-family: Georgia, serif;
  font-size: 12px;
  font-style: italic;
  color: var(--ink-light);
  margin-bottom: 8px;
}
.conn-item .conn-rel {
  font-size: 13px;
  color: var(--accent);
  letter-spacing: 0.05em;
  margin-bottom: 6px;
  font-weight: 500;
}
.conn-item .conn-desc {
  font-size: 13.5px;
  color: var(--ink-mid);
  line-height: 1.7;
}

/* ====== 致用列表 ====== */
.usage {
  display: grid;
  gap: 14px;
}
.usage-item {
  display: grid;
  grid-template-columns: 110px 1fr;
  gap: 18px;
  padding: 14px 0;
  border-bottom: 1px solid var(--line-soft);
}
.usage-item:last-child { border-bottom: 0; }
@media (max-width: 720px) {
  .usage-item { grid-template-columns: 1fr; gap: 4px; }
}
.usage-item .usage-key {
  font-weight: 600;
  font-size: 14px;
  color: var(--accent);
  letter-spacing: 0.1em;
}
.usage-item .usage-text {
  font-size: 15px;
  line-height: 1.8;
  color: var(--ink);
}

/* ====== 反观三问 ====== */
.reflect {
  background: var(--bg-soft);
  border: 1px dashed var(--ink-mid);
  padding: 28px 32px;
  margin: 16px 0;
}
.reflect .q {
  font-size: 16px;
  font-weight: 500;
  color: var(--ink);
  line-height: 1.8;
  letter-spacing: 0.02em;
  padding: 10px 0;
  border-bottom: 1px solid var(--line);
}
.reflect .q:last-child { border-bottom: 0; }
.reflect .q::before {
  content: counter(reflect-q) "　";
  counter-increment: reflect-q;
  color: var(--accent);
  font-family: Georgia, serif;
  font-weight: 400;
}
.reflect { counter-reset: reflect-q; }

/* ====== 延伸阅读 ====== */
.further {
  list-style: none;
  padding: 0;
}
.further li {
  padding: 12px 0;
  border-bottom: 1px solid var(--line-soft);
  font-size: 14.5px;
  line-height: 1.7;
}
.further li:last-child { border-bottom: 0; }
.further li a {
  color: var(--accent);
  text-decoration: none;
  border-bottom: 1px dotted var(--accent);
}
.further li a:hover { border-bottom-style: solid; }
.further .further-title {
  display: block;
  font-weight: 600;
  color: var(--ink);
  margin-bottom: 4px;
}
.further .further-meta {
  font-family: Georgia, serif;
  font-size: 12px;
  color: var(--ink-light);
  font-style: italic;
}

/* ====== 内联引用 ====== */
.quote-inline {
  background: var(--bg-soft);
  border-left: 3px solid var(--accent);
  padding: 10px 18px;
  margin: 12px 0;
  font-size: 15px;
  color: var(--ink);
  line-height: 1.8;
  font-style: italic;
}
.quote-inline strong { font-style: normal; }

/* ====== 翻页 ====== */
.pager {
  display: flex;
  justify-content: space-between;
  gap: 12px;
  margin-top: 64px;
  padding-top: 28px;
  border-top: 1px solid var(--line);
}
.pager a {
  flex: 1;
  padding: 16px 20px;
  text-decoration: none;
  color: var(--ink);
  background: var(--paper);
  border: 1px solid var(--line);
  transition: border-color 0.2s, background 0.2s;
  font-size: 14px;
}
.pager a:hover {
  border-color: var(--accent);
  background: var(--paper);
}
.pager a small {
  display: block;
  font-family: Georgia, serif;
  font-size: 11px;
  color: var(--ink-light);
  letter-spacing: 0.2em;
  text-transform: uppercase;
  margin-bottom: 4px;
}
.pager a.next { text-align: right; }
.pager a.disabled { opacity: 0.4; pointer-events: none; }

/* ====== 页脚 ====== */
.site-footer {
  margin-top: 64px;
  padding: 32px 0 16px;
  border-top: 1px solid var(--line);
  font-size: 12px;
  color: var(--ink-light);
  letter-spacing: 0.1em;
  text-align: center;
}
.site-footer .small {
  font-family: Georgia, serif;
  font-style: italic;
  margin-top: 6px;
  letter-spacing: 0.15em;
}

/* =========================================
   📚 首页：课程卡片列表
   ========================================= */
.home-hero {
  padding: 48px 0 56px;
  border-bottom: 1px solid var(--line);
  margin-bottom: 48px;
  text-align: center;
}
.home-hero .home-title {
  font-size: 64px;
  font-weight: 600;
  letter-spacing: 0.02em;
  color: var(--ink);
  margin-bottom: 12px;
}
.home-hero .home-title-en {
  font-family: Georgia, serif;
  font-size: 15px;
  font-style: italic;
  color: var(--ink-light);
  letter-spacing: 0.25em;
  text-transform: uppercase;
  margin-bottom: 22px;
}
.home-hero .home-tagline {
  font-size: 16px;
  color: var(--ink-mid);
  line-height: 1.85;
  max-width: 560px;
  margin: 0 auto;
}

/* 过滤标签 */
.filter-row {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  justify-content: center;
  margin-bottom: 40px;
}
.filter-tag {
  font-size: 13px;
  padding: 6px 14px;
  border: 1px solid var(--line);
  background: var(--paper);
  color: var(--ink-mid);
  cursor: pointer;
  text-decoration: none;
  letter-spacing: 0.05em;
  transition: all 0.2s;
}
.filter-tag:hover, .filter-tag.active {
  background: var(--ink);
  color: var(--bg);
  border-color: var(--ink);
}

/* 课程卡片列表 */
.lessons-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 16px;
}
.lesson-card {
  display: grid;
  grid-template-columns: 80px 1fr auto;
  gap: 24px;
  padding: 24px 28px;
  background: var(--paper);
  border: 1px solid var(--line);
  text-decoration: none;
  color: var(--ink);
  align-items: center;
  transition: border-color 0.2s, box-shadow 0.2s;
}
.lesson-card:hover {
  border-color: var(--accent);
  box-shadow: 0 2px 12px rgba(0,0,0,0.04);
}
@media (max-width: 720px) {
  .lesson-card { grid-template-columns: 1fr; gap: 8px; padding: 18px 20px; }
}

.lesson-card .lc-num {
  font-family: Georgia, serif;
  font-size: 28px;
  color: var(--accent);
  letter-spacing: 0.05em;
  text-align: center;
}
@media (max-width: 720px) {
  .lesson-card .lc-num { text-align: left; font-size: 18px; }
}

.lesson-card .lc-main .lc-name {
  font-size: 19px;
  font-weight: 600;
  color: var(--ink);
  margin-bottom: 4px;
  letter-spacing: 0.02em;
}
.lesson-card .lc-main .lc-name-en {
  font-family: Georgia, serif;
  font-size: 13px;
  font-style: italic;
  color: var(--ink-light);
  margin-bottom: 8px;
}
.lesson-card .lc-main .lc-meta {
  font-size: 12.5px;
  color: var(--ink-mid);
  letter-spacing: 0.04em;
}
.lesson-card .lc-main .lc-meta .lc-author {
  color: var(--ink);
  font-weight: 500;
  margin-right: 6px;
}
.lesson-card .lc-tag {
  font-size: 12px;
  background: var(--tag-bg);
  color: var(--ink-mid);
  padding: 4px 10px;
  letter-spacing: 0.1em;
  white-space: nowrap;
}
@media (max-width: 720px) {
  .lesson-card .lc-tag { justify-self: start; }
}

/* =========================================
   📱 移动端整体适配
   ========================================= */
@media (max-width: 720px) {
  .container { padding: 36px 18px 64px; }
  .container.wide { padding: 28px 16px 48px; }

  .site-header { margin-bottom: 32px; padding-bottom: 18px; }
  .site-header .logo { font-size: 21px; }
  .site-header .logo-en { font-size: 11px; letter-spacing: 0.2em; }

  .lesson-hero { padding: 20px 0 28px; margin-bottom: 36px; }
  .lesson-hero .lesson-title { font-size: 30px; line-height: 1.25; }
  .lesson-hero .lesson-title-en { font-size: 15px; }
  .lesson-hero .lesson-meta { gap: 12px 18px; font-size: 12.5px; }

  .section { margin-bottom: 42px; }
  .section-head { gap: 12px; margin-bottom: 18px; flex-wrap: wrap; }
  .section-head .sec-title { font-size: 19px; }
  .section-head .sec-en { width: 100%; margin-left: 0; order: 99; font-size: 10px; }

  .section p { font-size: 15.5px; line-height: 1.8; }
  .section ul li, .section ol li { font-size: 14.5px; }

  .theorem { padding: 22px 20px; }
  .theorem .theorem-body { font-size: 15.5px; }

  .commentary-card { padding: 18px 20px; }
  .commentary-card .comm-name { font-size: 14px; }
  .commentary-card p { font-size: 14.5px; }

  .case-card { padding: 18px 20px; }
  .case-card .case-meta { flex-wrap: wrap; gap: 8px 12px; }
  .case-card .case-title { font-size: 15.5px; }
  .case-card .case-when { margin-left: 0; }
  .case-card p { font-size: 14.5px; }

  .conn-item { padding: 14px 16px; }

  .reflect { padding: 22px 20px; }
  .reflect .q { font-size: 14.5px; }

  .further li { font-size: 13.5px; }

  .pager { flex-direction: column; gap: 8px; margin-top: 48px; }
  .pager a.next { text-align: left; }

  .home-hero { padding: 28px 0 32px; margin-bottom: 32px; }
  .home-hero .home-title { font-size: 44px; }
  .home-hero .home-title-en { font-size: 12px; }
  .home-hero .home-tagline { font-size: 14.5px; }

  .filter-row { gap: 6px; margin-bottom: 28px; }
  .filter-tag { font-size: 12px; padding: 5px 10px; }
}

@media (max-width: 380px) {
  .container { padding: 24px 14px 48px; }
  .lesson-hero .lesson-title { font-size: 26px; }
  .home-hero .home-title { font-size: 36px; }
  .theorem { padding: 18px 16px; }
}

/* 通用 */
.center { text-align: center; }
.muted { color: var(--ink-light); }
.mt-24 { margin-top: 24px; }
.mt-32 { margin-top: 32px; }
.mb-24 { margin-bottom: 24px; }