/* ======================================================
   蜗牛叔叔 · 全站共享样式
   common.css
   - 设计 tokens
   - body/container 基础
   - 顶部导航(含下拉菜单)
   - 页脚
   - 响应式 + 手机端汉堡菜单
====================================================== */

/* ------ DESIGN TOKENS · 博物馆白底质感 ------ */
:root {
  --bg: #ffffff;
  --bg-soft: #fafaf7;
  --bg-warm: #f5f1e8;
  --bg-card: #ffffff;
  --bg-dark: #1a1f1a;
  --ink: #1a1f1a;
  --ink-soft: #3d4339;
  --ink-dim: #8a8578;
  --line: #e8e3d5;
  --line-soft: #f0ebe0;

  /* 五类书系的博物馆色系 */
  --c-classic:    #b8502e;
  --c-classic-bg: #faeadd;
  --c-speak:      #5a7a3d;
  --c-speak-bg:   #eef2e4;
  --c-level:      #2d6a7f;
  --c-level-bg:   #e4eef1;
  --c-bridge:     #6b4a8a;
  --c-bridge-bg:  #ece4f2;
  --c-side:       #c88a3a;
  --c-side-bg:    #f7ecd8;

  /* 品牌深墨绿 */
  --brand: #2d4a3a;
  --brand-soft: #4a6b57;
  --brand-bg: #eaf0ec;
  --gold: #a88334;

  /* 辅助色 */
  --story: #b8502e;
  --story-soft: #d87550;
  --story-bg: #faeadd;
  --science: #2d6a7f;
  --science-soft: #4a8fa8;
  --science-bg: #e4eef1;
}

* { margin: 0; padding: 0; box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  font-family: 'Noto Serif SC', serif;
  background: var(--bg);
  color: var(--ink);
  font-size: 15px;
  line-height: 1.7;
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
}
body::before {
  content: '';
  position: fixed; inset: 0;
  background-image: url("data:image/svg+xml,%3Csvg viewBox='0 0 200 200' xmlns='http://www.w3.org/2000/svg'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='3' /%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)' opacity='0.4'/%3E%3C/svg%3E");
  opacity: 0.08;
  pointer-events: none;
  z-index: 1;
  mix-blend-mode: multiply;
}

.container {
  max-width: 1320px;
  margin: 0 auto;
  padding: 0 48px;
  position: relative;
  z-index: 2;
}

/* ======================================================
   TOP BAR · 顶部导航
====================================================== */
.topbar {
  padding: 24px 0;
  border-bottom: 1px solid var(--ink);
  font-family: 'JetBrains Mono', monospace;
  font-size: 11px;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  background: var(--bg);
  position: relative;
  z-index: 50;
}
.topbar .container {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

/* Logo */
.topbar .logo {
  display: inline-flex;
  align-items: center;
  flex: 0 0 auto;
  line-height: 0;
  text-decoration: none;
}
.topbar .logo::before {
  content: none;
}
.topbar .logo img {
  display: block;
  width: 221px;
  height: auto;
}

/* Nav · 桌面端 */
.topbar .nav {
  display: flex;
  gap: 36px;
  color: var(--ink-dim);
  align-items: center;
}
.topbar .nav-item {
  position: relative;
}
.topbar .nav-item > a,
.topbar .nav-item > button {
  color: inherit;
  text-decoration: none;
  background: transparent;
  border: 0;
  font-family: inherit;
  font-size: inherit;
  letter-spacing: inherit;
  text-transform: inherit;
  cursor: pointer;
  padding: 6px 0;
  display: inline-flex;
  align-items: center;
  gap: 6px;
  transition: color 0.2s;
}
.topbar .nav-item > a:hover,
.topbar .nav-item > button:hover,
.topbar .nav-item.active > a,
.topbar .nav-item.active > button {
  color: var(--ink);
}

/* 下拉箭头 */
.topbar .nav-item .caret {
  font-size: 9px;
  opacity: 0.6;
  transition: transform 0.2s;
  line-height: 1;
}
.topbar .nav-item.open .caret,
.topbar .nav-item:hover .caret {
  transform: rotate(180deg);
}

/* 下拉菜单 */
.topbar .dropdown {
  position: absolute;
  top: calc(100% + 18px);
  left: -20px;
  min-width: 220px;
  background: var(--bg);
  border: 1px solid var(--line);
  box-shadow: 0 10px 30px -10px rgba(26, 31, 26, 0.18);
  padding: 10px 0;
  opacity: 0;
  visibility: hidden;
  transform: translateY(-6px);
  transition: opacity 0.2s, visibility 0.2s, transform 0.2s;
  z-index: 60;
  text-transform: none;
  letter-spacing: 0;
}
.topbar .nav-item:last-child .dropdown {
  left: auto;
  right: 0;
}
/* Hover 桥接区 · 让鼠标移动到下拉菜单过程中不会因进入间隙而关闭 */
.topbar .nav-item::after {
  content: '';
  position: absolute;
  top: 100%;
  left: -20px;
  right: -20px;
  height: 18px;
  display: none;
}
.topbar .nav-item.has-dropdown:hover::after,
.topbar .nav-item.open::after {
  display: block;
}
.topbar .nav-item:hover .dropdown,
.topbar .nav-item.open .dropdown,
.topbar .nav-item .dropdown:hover {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}

.topbar .dropdown a {
  display: block;
  padding: 10px 22px;
  font-family: 'Noto Serif SC', serif;
  font-size: 14px;
  font-weight: 400;
  letter-spacing: 0;
  text-transform: none;
  color: var(--ink-soft);
  text-decoration: none;
  transition: background 0.15s, color 0.15s;
}
.topbar .dropdown a:hover,
.topbar .dropdown a.active {
  color: var(--ink);
  background: var(--bg-warm);
}
.topbar .dropdown .caption {
  display: block;
  font-size: 10px;
  color: var(--ink-dim);
  font-family: 'JetBrains Mono', monospace;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  margin-top: 2px;
  font-weight: 400;
}

/* 手机端汉堡按钮 */
.topbar .hamburger {
  display: none;
  width: 28px;
  height: 28px;
  background: transparent;
  border: 0;
  cursor: pointer;
  position: relative;
  padding: 0;
}
.topbar .hamburger span {
  display: block;
  width: 22px;
  height: 1.5px;
  background: var(--ink);
  position: absolute;
  left: 3px;
  transition: all 0.3s;
}
.topbar .hamburger span:nth-child(1) { top: 7px; }
.topbar .hamburger span:nth-child(2) { top: 13px; }
.topbar .hamburger span:nth-child(3) { top: 19px; }
.topbar.menu-open .hamburger span:nth-child(1) {
  top: 13px; transform: rotate(45deg);
}
.topbar.menu-open .hamburger span:nth-child(2) { opacity: 0; }
.topbar.menu-open .hamburger span:nth-child(3) {
  top: 13px; transform: rotate(-45deg);
}

/* ======================================================
   FOOTER · 页脚
====================================================== */
footer {
  padding: 80px 0 40px;
  margin-top: 40px;
  border-top: 1px solid var(--ink);
  position: relative;
  z-index: 2;
}
footer .container {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-family: 'JetBrains Mono', monospace;
  font-size: 11px;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  color: var(--ink-dim);
}
footer .logo-sig {
  font-family: 'Fraunces', serif;
  font-style: italic;
  font-size: 18px;
  color: var(--ink);
  text-transform: none;
  letter-spacing: 0;
}

/* ======================================================
   RESPONSIVE
====================================================== */

/* ------ 平板 ≤ 1024px ------ */
@media (max-width: 1024px) {
  .container { padding: 0 32px; }
  .topbar .nav { gap: 24px; }
}

/* ------ 手机 ≤ 720px ------ */
@media (max-width: 720px) {
  .container { padding: 0 20px; }

  .topbar { padding: 14px 0; font-size: 10px; }
  .topbar .logo img { width: 188px; }

  /* 隐藏桌面端水平导航,显示汉堡按钮 */
  .topbar .nav {
    display: none;
  }
  .topbar .hamburger { display: block; }

  /* 菜单展开时 · 导航变成全屏下拉面板 */
  .topbar.menu-open .nav {
    display: flex;
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    background: var(--bg);
    border-bottom: 1px solid var(--ink);
    padding: 12px 0;
    box-shadow: 0 20px 30px -20px rgba(26, 31, 26, 0.2);
  }
  .topbar.menu-open .nav-item {
    border-bottom: 1px solid var(--line-soft);
  }
  .topbar.menu-open .nav-item:last-child {
    border-bottom: 0;
  }
  .topbar.menu-open .nav-item > a,
  .topbar.menu-open .nav-item > button {
    padding: 14px 20px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    width: 100%;
    color: var(--ink);
    font-size: 13px;
  }

  /* 手机端下拉菜单 · 改为收起展开风格(不是 hover) */
  .topbar.menu-open .dropdown {
    position: static;
    min-width: 0;
    border: 0;
    box-shadow: none;
    background: var(--bg-soft);
    padding: 0;
    opacity: 1;
    visibility: visible;
    transform: none;
    transition: none;
    display: none;
  }
  .topbar.menu-open .nav-item.open .dropdown {
    display: block;
  }
  /* 非 open 的 nav-item 在手机端永远不显示下拉(覆盖桌面 hover 规则) */
  .topbar.menu-open .nav-item:hover .dropdown {
    display: none;
  }
  .topbar.menu-open .nav-item.open:hover .dropdown,
  .topbar.menu-open .nav-item.open .dropdown {
    display: block;
  }
  .topbar.menu-open .dropdown a {
    padding: 12px 36px;
    font-size: 13px;
  }

  footer { padding: 48px 0 24px; margin-top: 32px; }
  footer .container {
    flex-direction: column;
    gap: 10px;
    text-align: center;
    font-size: 10px;
  }
  footer .logo-sig { font-size: 16px; }
}