/* ============================================================
   信奥教学练网站 - 全局样式
   配色：浅蓝 #E6F7FF + 浅黄 #FFF9E6 + 浅绿 #E6FFE6
   说明：纯静态，无外链字体/图片，全部使用 SVG 内联图标
   ============================================================ */

:root {
  --blue-bg: #E6F7FF;      /* 浅蓝背景 */
  --blue-main: #4A9FE8;    /* 主蓝 */
  --blue-deep: #2E7CC4;    /* 深蓝 */
  --yellow-bg: #FFF9E6;    /* 浅黄背景 */
  --yellow-main: #F5C453;  /* 主黄 */
  --green-bg: #E6FFE6;     /* 浅绿背景 */
  --green-main: #5CB85C;   /* 主绿 */
  --orange-main: #F59A4A;  /* 强调橙 */
  --red-main: #E86A5E;     /* 警示红 */
  --text-main: #2D3A4A;    /* 正文主色 */
  --text-sub: #6B7A8C;     /* 次要文字 */
  --card-bg: #FFFFFF;      /* 卡片背景 */
  --border: #DCEAF5;       /* 边框 */
  --code-bg: #232B3B;      /* 代码块深色背景 */
  --shadow: 0 2px 10px rgba(74, 159, 232, 0.12);
  --radius: 14px;
  --font-main: "Microsoft YaHei", "微软雅黑", "SimSun", "宋体", sans-serif;
  --font-mono: "Consolas", "Courier New", monospace;
}

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

html { scroll-behavior: smooth; }

body {
  font-family: var(--font-main);
  font-size: 14px;
  color: var(--text-main);
  background:
    radial-gradient(circle at 8% 10%, rgba(74,159,232,0.10), transparent 260px),
    radial-gradient(circle at 92% 30%, rgba(245,196,83,0.12), transparent 280px),
    radial-gradient(circle at 12% 85%, rgba(92,184,92,0.10), transparent 260px),
    linear-gradient(180deg, #F4FAFF 0%, #EFF7FF 100%);
  min-height: 100vh;
  line-height: 1.75;
}

a { color: var(--blue-deep); text-decoration: none; }
a:hover { text-decoration: none; }

/* ---------------- 顶部导航 ---------------- */
.top-nav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(255, 255, 255, 0.92);
  backdrop-filter: blur(6px);
  border-bottom: 2px solid var(--border);
  box-shadow: 0 2px 8px rgba(74,159,232,0.08);
  transition: transform .3s ease;
}
/* 向下滚动时隐藏导航栏（由 script.js 控制） */
.top-nav.hidden { transform: translateY(-100%); }
.nav-inner {
  max-width: 1200px;
  margin: 0 auto;
  padding: 10px 20px;
  display: flex;
  align-items: center;
  gap: 14px;
  flex-wrap: nowrap;
}
.nav-logo {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 18px;
  font-weight: bold;
  color: var(--blue-deep);
}
.nav-logo .logo-icon {
  width: 34px; height: 34px;
  background: linear-gradient(135deg, var(--blue-main), #7FC4F5);
  border-radius: 10px;
  display: flex; align-items: center; justify-content: center;
  box-shadow: var(--shadow);
}
.nav-links { display: flex; gap: 8px; margin-left: auto; flex-wrap: nowrap; }
.nav-links a {
  padding: 6px 14px;
  border-radius: 20px;
  background: var(--blue-bg);
  color: var(--blue-deep);
  font-weight: 600;
  border: 1px solid var(--border);
  transition: all .2s;
}
.nav-links a:hover { background: var(--blue-main); color: #fff; text-decoration: none; transform: translateY(-1px); box-shadow: 0 3px 8px rgba(74,159,232,0.22); }
.nav-links a.active {
  background: linear-gradient(135deg, var(--blue-main), #7FC4F5);
  color: #fff;
  border-color: transparent;
  box-shadow: 0 3px 8px rgba(74,159,232,0.30);
}

/* ---------------- 内容容器 ---------------- */
.container { max-width: 1200px; margin: 0 auto; padding: 24px 20px 60px; }

/* ---------------- 面包屑 ---------------- */
.crumbs {
  font-size: 13px;
  color: var(--text-sub);
  background: #fff;
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 8px 16px;
  margin-bottom: 18px;
  display: inline-block;
}

/* ---------------- 页面大标题 ---------------- */
.page-title {
  text-align: center;
  margin: 26px 0 10px;
}
.page-title h1 {
  font-size: 26px;
  color: var(--blue-deep);
  letter-spacing: 1px;
}
.page-title .sub { color: var(--text-sub); font-size: 14px; margin-top: 4px; }

/* ---------------- 卡片 ---------------- */
.card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 22px 26px;
  margin-bottom: 22px;
}
.card h2 {
  font-size: 19px;
  color: var(--blue-deep);
  margin-bottom: 14px;
  display: flex;
  align-items: center;
  gap: 10px;
}
.card h3 {
  font-size: 16px;
  color: var(--text-main);
  margin: 16px 0 8px;
}
.card h2 .section-badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: linear-gradient(135deg, var(--blue-main), #7FC4F5);
  color: #fff;
  font-size: 13px;
  padding: 3px 12px;
  border-radius: 20px;
  white-space: nowrap;
}
.section-badge.green { background: linear-gradient(135deg, var(--green-main), #8BD18B); }
.section-badge.yellow { background: linear-gradient(135deg, var(--yellow-main), #F7D37C); }
.section-badge.orange { background: linear-gradient(135deg, var(--orange-main), #F7B774); }

/* ---------------- 学习目标 ---------------- */
.goal-list { list-style: none; }
.goal-list li {
  position: relative;
  padding: 6px 0 6px 30px;
  margin-bottom: 4px;
}
.goal-list li::before {
  content: "";
  position: absolute;
  left: 4px; top: 11px;
  width: 16px; height: 16px;
  background: var(--yellow-main);
  border-radius: 50%;
  box-shadow: inset 0 0 0 3px #fff;
}
.goal-meta {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
  margin-bottom: 12px;
}
.goal-meta .tag {
  background: var(--yellow-bg);
  border: 1px solid #F7E4B8;
  color: #8a6d1a;
  padding: 3px 12px;
  border-radius: 20px;
  font-size: 13px;
}

/* ---------------- 知识点 ---------------- */
.knowledge-item {
  border-left: 4px solid var(--blue-main);
  background: #F6FBFF;
  border-radius: 0 10px 10px 0;
  padding: 14px 18px;
  margin: 14px 0;
}
.knowledge-item h4 { font-size: 15px; color: var(--blue-deep); margin-bottom: 6px; }
.knowledge-item p { margin: 6px 0; }

/* 思考题 */
.think-box {
  background: var(--green-bg);
  border: 1px dashed var(--green-main);
  border-radius: 10px;
  padding: 12px 16px;
  margin: 12px 0;
}
.think-box .think-title { color: var(--green-main); font-weight: bold; margin-bottom: 4px; }

/* ---------------- 代码块 ---------------- */
.code-block { position: relative; margin: 12px 0; }
.code-block pre {
  background: var(--code-bg);
  color: #E6EDF7;
  border-radius: 10px;
  padding: 14px 16px;
  overflow-x: auto;
  font-family: var(--font-mono);
  font-size: 13.5px;
  line-height: 1.6;
  tab-size: 4;
}
.code-block .copy-btn {
  position: absolute;
  top: 8px; right: 8px;
  background: rgba(255,255,255,0.14);
  color: #fff;
  border: none;
  border-radius: 8px;
  padding: 4px 10px;
  font-size: 12px;
  cursor: pointer;
  transition: all .2s;
  opacity: 0.75;
}
.code-block .copy-btn:hover { background: var(--blue-main); opacity: 1; }
.code-block .copy-btn.copied { background: var(--green-main); }

/* 代码高亮配色 */
.code-block .tok-kw   { color: #C792EA; font-weight: 600; }   /* 关键字 */
.code-block .tok-type { color: #82AAFF; }                     /* 类型 */
.code-block .tok-str  { color: #C3E88D; }                     /* 字符串 */
.code-block .tok-com  { color: #6B7A8C; font-style: italic; } /* 注释 */
.code-block .tok-num  { color: #F78C6C; }                     /* 数字 */
.code-block .tok-fn   { color: #82AAFF; }                     /* 函数 */
.code-block .tok-std  { color: #F5C453; }                     /* cout/cin/endl 等 */
.code-block .tok-pre  { color: #7FC4F5; }                     /* 预处理 */
.code-block .tok-op   { color: #89DDFF; }                     /* 运算符 */

/* C++ 代码块行号 */
.code-block .code-line { display: block; position: relative; padding-left: 3.4em; min-height: 1.6em; }
.code-block .ln {
  position: absolute;
  left: 0; top: 0;
  width: 2.6em;
  text-align: right;
  color: #6B7A8C;
  padding-right: 0.7em;
  border-right: 1px solid rgba(255,255,255,0.14);
  user-select: none;
  -webkit-user-select: none;
  box-sizing: border-box;
}

/* ---------------- 练习区 ---------------- */
.quiz-item {
  background: #FBFDFF;
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 14px 18px;
  margin: 12px 0;
}
.quiz-item .q-title { font-weight: 600; margin-bottom: 8px; color: var(--text-main); }
.quiz-item .options { list-style: none; }
.quiz-item .options li { padding: 4px 0 4px 6px; }
.quiz-item .options li b { color: var(--blue-deep); margin-right: 4px; }

.answer-btn {
  margin-top: 10px;
  background: var(--green-main);
  color: #fff;
  border: none;
  border-radius: 20px;
  padding: 7px 20px;
  font-size: 13px;
  cursor: pointer;
  transition: all .2s;
  font-family: var(--font-main);
}
.answer-btn:hover { background: #4aa64a; transform: translateY(-1px); }
.answer-body {
  display: none;
  margin-top: 10px;
  background: var(--green-bg);
  border: 1px solid #BFE5BF;
  border-radius: 8px;
  padding: 12px 16px;
}
.answer-body.show { display: block; animation: fadeIn .3s ease; }
.answer-body .ans-label { color: var(--green-main); font-weight: bold; }

@keyframes fadeIn { from { opacity: 0; transform: translateY(-4px); } to { opacity: 1; transform: none; } }

/* ---------------- 教师参考（可折叠） ---------------- */
details.teacher-ref {
  background: var(--yellow-bg);
  border: 1px solid #F2E2B8;
  border-radius: var(--radius);
  margin-bottom: 22px;
  overflow: hidden;
}
details.teacher-ref summary {
  cursor: pointer;
  padding: 14px 22px;
  font-size: 16px;
  font-weight: bold;
  color: #8a6d1a;
  list-style: none;
  display: flex;
  align-items: center;
  gap: 10px;
  user-select: none;
}
details.teacher-ref summary::-webkit-details-marker { display: none; }
details.teacher-ref summary::before {
  content: "▶";
  font-size: 12px;
  transition: transform .2s;
  color: var(--yellow-main);
}
details.teacher-ref[open] summary::before { transform: rotate(90deg); }
details.teacher-ref .ref-body { padding: 0 22px 20px; }
.ref-block { margin: 12px 0; padding-left: 12px; border-left: 3px solid #F2E2B8; }
.ref-block .ref-tag {
  display: inline-block;
  background: #fff;
  border: 1px solid #F2E2B8;
  color: #8a6d1a;
  border-radius: 14px;
  padding: 1px 12px;
  font-size: 12px;
  font-weight: bold;
  margin-right: 8px;
  margin-bottom: 4px;
}

/* 重点回顾 · 问答折叠（点击展开讲解/答案） */
details.ref-qa {
  background: #fff;
  border: 1px solid #F2E2B8;
  border-radius: 10px;
  margin: 10px 0;
  overflow: hidden;
  box-shadow: 0 1px 4px rgba(245, 196, 83, 0.10);
  transition: box-shadow .2s;
}
details.ref-qa[open] { box-shadow: 0 2px 8px rgba(245, 196, 83, 0.18); }
details.ref-qa summary {
  cursor: pointer;
  list-style: none;
  padding: 10px 16px;
  font-weight: 600;
  color: var(--blue-deep);
  display: flex;
  align-items: center;
  gap: 8px;
  user-select: none;
  transition: background .2s;
}
details.ref-qa summary::-webkit-details-marker { display: none; }
details.ref-qa summary::before { content: "💡"; font-size: 14px; }
details.ref-qa summary::after {
  content: "▾ 点击查看讲解";
  margin-left: auto;
  font-size: 12px;
  font-weight: normal;
  color: #c08514;
  background: var(--yellow-bg);
  border: 1px solid #F7E4B8;
  border-radius: 12px;
  padding: 1px 10px;
  white-space: nowrap;
}
details.ref-qa[open] summary { background: #FFFDF5; }
details.ref-qa[open] summary::after {
  content: "▴ 收起讲解";
  background: var(--yellow-main);
  color: #fff;
  border-color: var(--yellow-main);
}
details.ref-qa .qa-ans {
  padding: 10px 16px 14px;
  color: var(--text-main);
  font-size: 13.5px;
  border-top: 1px dashed #F2E2B8;
  margin: 0 8px 10px;
  padding-top: 10px;
  animation: fadeIn .25s ease;
}
details.ref-qa .qa-ans b { color: var(--green-main); }

/* ---------------- 上一课/下一课 ---------------- */
.lesson-nav {
  display: flex;
  justify-content: space-between;
  gap: 14px;
  margin-top: 8px;
}
.lesson-nav a {
  flex: 1;
  background: #fff;
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 12px 16px;
  text-align: center;
  color: var(--blue-deep);
  font-weight: 600;
  box-shadow: var(--shadow);
  transition: all .2s;
}
.lesson-nav a:hover { background: var(--blue-bg); transform: translateY(-1px); text-decoration: none; }
.lesson-nav a.disabled { opacity: 0.4; pointer-events: none; }

/* ---------------- 首页英雄区 ---------------- */
.hero {
  background: linear-gradient(135deg, var(--blue-bg), #F0F9FF 55%, var(--yellow-bg));
  border: 1px solid var(--border);
  border-radius: 20px;
  padding: 46px 40px;
  text-align: center;
  margin: 20px 0 30px;
  box-shadow: var(--shadow);
}
.hero .robot { font-size: 64px; line-height: 1; margin-bottom: 10px; }
.hero h1 { font-size: 30px; color: var(--blue-deep); margin-bottom: 10px; }
.hero p { color: var(--text-sub); font-size: 15px; max-width: 640px; margin: 0 auto 18px; }
.hero .cta {
  display: inline-block;
  background: linear-gradient(135deg, var(--blue-main), #7FC4F5);
  color: #fff;
  padding: 12px 34px;
  border-radius: 30px;
  font-size: 16px;
  font-weight: bold;
  box-shadow: 0 4px 14px rgba(74,159,232,0.35);
  transition: all .2s;
}
.hero .cta:hover { transform: translateY(-2px); text-decoration: none; }

/* ---------------- 级别卡片 ---------------- */
.level-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 18px;
}
.level-card {
  background: #fff;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 22px 20px;
  text-align: center;
  box-shadow: var(--shadow);
  transition: all .2s;
}
.level-card:hover { transform: translateY(-4px); box-shadow: 0 8px 20px rgba(74,159,232,0.18); }
.level-card .lv-icon { font-size: 40px; margin-bottom: 8px; }
.level-card h3 { color: var(--blue-deep); font-size: 18px; margin-bottom: 6px; }
.level-card p { color: var(--text-sub); font-size: 13px; margin-bottom: 10px; }
.level-card .lv-tag {
  display: inline-block;
  background: var(--blue-bg);
  color: var(--blue-deep);
  border-radius: 16px;
  padding: 2px 14px;
  font-size: 12px;
  font-weight: bold;
}
.level-card .lv-tag.green { background: var(--green-bg); color: #3f8f3f; }
.level-card .lv-tag.yellow { background: var(--yellow-bg); color: #8a6d1a; }
.level-card .lv-tag.orange { background: #FFF0E6; color: #c06b1e; }

/* ---------------- 课程序列表 ---------------- */
.course-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(220px, 1fr));
  gap: 14px;
}
.course-item {
  display: flex;
  align-items: center;
  gap: 12px;
  background: #fff;
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 12px 16px;
  box-shadow: var(--shadow);
  transition: all .2s;
}
.course-item:hover { transform: translateY(-3px); box-shadow: 0 8px 18px rgba(74,159,232,0.16); text-decoration: none; }
.course-item .num {
  min-width: 38px; height: 38px;
  background: linear-gradient(135deg, var(--blue-main), #7FC4F5);
  color: #fff;
  border-radius: 50%;
  display: flex; align-items: center; justify-content: center;
  font-weight: bold;
  font-size: 14px;
}
.course-item .name { font-weight: 600; color: var(--text-main); font-size: 14px; }
.course-item .lock-ico { margin-left: auto; font-size: 13px; opacity: .85; }
.course-item.locked {
  opacity: .6;
  background: #f4f6f8;
  border-color: #e3e8ee;
  box-shadow: none;
  cursor: not-allowed;
}
.course-item.locked:hover { transform: none; box-shadow: none; }
.course-item.locked .num { background: #c3ccd6; }
.course-item.locked .name { color: #9aa5b1; }

/* ---------------- 页脚 ---------------- */
.footer {
  text-align: center;
  color: var(--text-sub);
  font-size: 13px;
  padding: 30px 20px;
}

/* ---------------- 提示框 ---------------- */
.notice {
  background: var(--yellow-bg);
  border: 1px solid #F2E2B8;
  border-radius: 10px;
  padding: 12px 16px;
  margin: 14px 0;
  color: #8a6d1a;
}

/* ---------------- 标记学完 ---------------- */
.done-label{display:inline-flex;align-items:center;gap:6px;background:#fff;border:1px solid var(--border);border-radius:20px;padding:5px 14px;font-size:13px;color:var(--text-sub);cursor:pointer;margin-top:8px}
.done-label input{accent-color:var(--green-main);width:15px;height:15px}

/* ---------------- 图案 / 输出样例 ---------------- */
.tree-art{font-family:var(--font-mono);background:#F6FBFF;border:1px solid var(--border);border-radius:10px;padding:14px 18px;line-height:1.5;display:inline-block;white-space:pre}

/* ---------------- 数据表格（vocab-table） ---------------- */
.vocab-table {
  display: block;               /* 超宽时整表横向滚动，避免挤压 */
  width: 100%;
  max-width: 100%;
  margin: 14px 0;
  border-collapse: separate;
  border-spacing: 0;
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
  background: #fff;
  border: 1px solid var(--border);
  border-radius: 12px;
  box-shadow: 0 2px 10px rgba(74,159,232,0.10);
  font-size: 14px;
  line-height: 1.65;
  color: var(--text-main);
}
.vocab-table th,
.vocab-table td {
  padding: 10px 16px;
  border-right: 1px solid #E6F0F8;
  border-bottom: 1px solid #E6F0F8;
  text-align: center;
  vertical-align: middle;
}
.vocab-table th:last-child,
.vocab-table td:last-child { border-right: none; }
.vocab-table tr:last-child th,
.vocab-table tr:last-child td { border-bottom: none; }

/* 表头：渐变蓝 + 白字 */
.vocab-table th {
  background: linear-gradient(135deg, var(--blue-main), #7FC4F5);
  color: #fff;
  font-weight: 700;
  letter-spacing: .5px;
  white-space: nowrap;
  border-right-color: rgba(255,255,255,0.20);
  border-bottom-color: rgba(255,255,255,0.35);
}

/* 圆角（separate 模式下由四角单元格撑起） */
.vocab-table th:first-child { border-top-left-radius: 11px; }
.vocab-table th:last-child  { border-top-right-radius: 11px; }
.vocab-table tr:last-child td:first-child { border-bottom-left-radius: 11px; }
.vocab-table tr:last-child td:last-child  { border-bottom-right-radius: 11px; }

/* 斑马纹 */
.vocab-table tr:nth-child(even) td { background: #F4FAFF; }

/* 首列：行标签列 */
.vocab-table td:first-child {
  background: #EFF6FE;
  color: var(--blue-deep);
  font-weight: 600;
  white-space: nowrap;
}
.vocab-table tr:nth-child(even) td:first-child { background: #E5F1FC; }

/* 末列：公式 / 代码 / 关键结果列 */
.vocab-table th:last-child,
.vocab-table td:last-child { font-family: var(--font-mono); }
.vocab-table td:last-child { background: var(--yellow-bg); }
.vocab-table tr:nth-child(even) td:last-child { background: #FFF4D6; }

/* 空单元格：浅斜纹占位 */
.vocab-table th:empty,
.vocab-table td:empty {
  background: repeating-linear-gradient(45deg, rgba(74,159,232,0.06) 0 5px, transparent 5px 10px);
}

/* 行悬停高亮 */
.vocab-table tr:hover td { background: #FFF7E0; }
.vocab-table tr:hover td:first-child { background: #FFEFC6; }
.vocab-table tr:hover td:last-child { background: #FFEAB2; }

/* 含代码 / 换行的长内容单元格左对齐，更易读 */
.vocab-table td:has(code),
.vocab-table td:has(br) { text-align: left; }

/* 导航页已完成课程打勾样式 */
.course-item.done { border-color: var(--green-main); background: #F2FFF2; }
.course-item.done .num { background: linear-gradient(135deg, var(--green-main), #8BD18B); }
.course-item.done .name::after { content: " ✓"; color: var(--green-main); font-weight: bold; }

/* ---------------- 词汇记忆（vocab） ---------------- */
/* 徽章：紫色渐变（需高于 .card h2 .section-badge 的特异性） */
.card h2 .section-badge.purple,
.vocab-card h2 .section-badge {
  background: linear-gradient(135deg, #9B6BF3, #B48CF8);
}
/* 早期版标题（c1 前几课） */
.vocab-h3 {
  font-size: 16px;
  color: #7A4FD0;
  margin: 18px 0 12px;
  padding-left: 10px;
  border-left: 4px solid #9B6BF3;
}
/* 单词条目卡片（新结构 vocab-item + 旧结构 knowledge-item 统一） */
.vocab-item,
.vocab-h3 ~ .knowledge-item {
  background: #FBF8FF;
  border: 1px solid #EBDFFB;
  border-left: 4px solid #9B6BF3;
  border-radius: 10px;
  padding: 12px 16px;
  margin: 10px 0;
  box-shadow: 0 1px 4px rgba(155,107,243,0.08);
  transition: all .2s;
}
.vocab-item:hover,
.vocab-h3 ~ .knowledge-item:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(155,107,243,0.16);
  border-color: #D3BCF7;
}
/* 单词名徽章 */
.vocab-word,
.vocab-h3 ~ .knowledge-item h4 {
  display: inline-block;
  background: linear-gradient(135deg, #9B6BF3, #B48CF8);
  color: #fff;
  font-family: var(--font-mono);
  font-weight: 700;
  font-size: 15px;
  padding: 3px 14px;
  border-radius: 16px;
  margin-bottom: 8px;
  letter-spacing: .5px;
  box-shadow: 0 2px 6px rgba(155,107,243,0.28);
}
/* 含义 / 用法标签 */
.vocab-item p b,
.vocab-h3 ~ .knowledge-item p b {
  color: #7A4FD0;
}
/* 条目内代码 */
.vocab-item code,
.vocab-h3 ~ .knowledge-item code {
  background: #F0E7FD;
  color: #6B3FC8;
  padding: 1px 6px;
  border-radius: 6px;
  font-family: var(--font-mono);
  font-size: 13px;
}
/* 表格版卡片装饰 */
.vocab-card {
  border-top: 3px solid #9B6BF3;
}
.vocab-card .vocab-table {
  margin-top: 4px;
}

/* 小屏适配（主目标 1200px 内） */
@media (max-width: 760px) {
  .container { padding: 16px 12px 50px; }
  .card { padding: 16px; }
  .hero { padding: 30px 20px; }
  .hero h1 { font-size: 24px; }
  .top-nav { overflow-x: auto; }
  .top-nav .nav-inner { min-width: 760px; }
  .nav-links a { padding: 5px 10px; font-size: 13px; }
  .level-grid { grid-template-columns: repeat(2, 1fr); }
  .vocab-table th,
  .vocab-table td { padding: 8px 10px; font-size: 13px; }
}
@media (max-width: 520px) {
  .level-grid { grid-template-columns: 1fr; }
  .nav-links a { padding: 4px 8px; font-size: 12px; }
  .ref-qa summary { padding: 8px 12px; }
}

/* ================ 会员系统扩展样式 ================ */
/* 顶部导航用户区 */
.nav-user { display: flex; align-items: center; gap: 8px; margin-left: 6px; flex-wrap: nowrap; }
.nav-user a { text-decoration: none; }
.nav-login, .nav-reg {
  padding: 5px 14px; border-radius: 20px; font-weight: 600; font-size: 13px;
  transition: all .2s;
}
.nav-login { background: #fff; color: var(--blue-deep); border: 1px solid var(--blue-main); }
.nav-login:hover { background: var(--blue-bg); }
.nav-reg { background: linear-gradient(135deg, var(--blue-main), #7FC4F5); color: #fff; border: 1px solid transparent; }
.nav-reg:hover { transform: translateY(-1px); box-shadow: 0 3px 8px rgba(74,159,232,.3); }
.nav-username { color: var(--blue-deep); font-weight: 700; font-size: 13px; }
.nav-username:hover { text-decoration: underline; }
.nav-logout { color: #999; font-size: 12px; padding: 4px 8px; border: 1px solid var(--border); border-radius: 14px; }
.nav-logout:hover { color: #c0392b; border-color: #e0b0b0; }
.nav-badge {
  display: inline-block; padding: 2px 9px; border-radius: 12px; font-size: 11px; font-weight: 700; line-height: 1.6;
}
.nav-badge.vip { background: linear-gradient(135deg,#f6c453,#f0a32c); color: #fff; }
.nav-badge.admin { background: linear-gradient(135deg,#5C6BC0,#7986CB); color: #fff; }
.nav-admin-link { font-size: 12px; color: #5C6BC0; border: 1px solid #c5cae9; padding: 3px 10px; border-radius: 14px; }
.nav-admin-link:hover { background: #e8eaf6; }

/* 顶部导航用户下拉菜单 */
.nav-user-drop { position: relative; }
.nav-username-drop {
  display: flex; align-items: center; gap: 6px;
  background: #fff; border: 1px solid var(--border); border-radius: 20px;
  padding: 4px 12px; cursor: pointer; font-family: inherit;
  font-weight: 700; font-size: 13px; color: var(--blue-deep);
  transition: all .2s; white-space: nowrap;
}
.nav-username-drop:hover { background: var(--blue-bg); }
.nav-username-drop .nav-avatar { font-size: 14px; line-height: 1; }
.nav-username-drop .caret { font-size: 10px; color: #999; transition: transform .2s; }
.nav-user-drop.open .nav-username-drop .caret { transform: rotate(180deg); }
.nav-dropdown {
  position: absolute; right: 0; top: calc(100% + 10px);
  min-width: 200px; background: #fff; border: 1px solid var(--border);
  border-radius: 12px; box-shadow: 0 12px 32px rgba(20,40,80,.14);
  padding: 6px; z-index: 300; display: none;
}
.nav-user-drop.open .nav-dropdown { display: block; animation: dd-fade .15s ease; }
@keyframes dd-fade { from { opacity: 0; transform: translateY(-4px); } to { opacity: 1; transform: none; } }
.nav-dropdown a {
  display: flex; align-items: center; gap: 10px;
  padding: 9px 12px; border-radius: 8px; font-size: 13.5px;
  color: var(--text-main); font-weight: 500; white-space: nowrap;
}
.nav-dropdown a:hover { background: var(--blue-bg); color: var(--blue-deep); }
.nav-dropdown .dd-ico { font-size: 15px; width: 20px; text-align: center; }
.nav-dropdown .nav-drop-divider { height: 1px; background: var(--border); margin: 6px 8px; }
.nav-dropdown a.drop-danger { color: #c0392b; }
.nav-dropdown a.drop-danger:hover { background: #ffecec; color: #c0392b; }

/* 个人中心子页导航 */
.uc-tabs {
  display: flex; gap: 6px; flex-wrap: wrap;
  background: #fff; border: 1px solid var(--border); border-radius: 12px;
  padding: 6px; margin-bottom: 20px;
}
.uc-tab {
  display: flex; align-items: center; gap: 6px;
  padding: 7px 16px; border-radius: 8px; font-size: 13.5px; font-weight: 600;
  color: var(--text-sub); transition: all .2s;
}
.uc-tab:hover { background: var(--blue-bg); color: var(--blue-deep); text-decoration: none; }
.uc-tab.active { background: linear-gradient(135deg, var(--blue-main), #7FC4F5); color: #fff; box-shadow: 0 3px 8px rgba(74,159,232,.25); }
.uc-ico { font-size: 15px; }

/* 个人中心快捷功能入口 */
.uc-quick-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(230px, 1fr)); gap: 12px; }
.uc-quick {
  display: flex; flex-direction: column; gap: 4px;
  background: var(--blue-bg); border: 1px solid var(--border); border-radius: 12px;
  padding: 16px 18px; transition: all .2s;
}
.uc-quick:hover { transform: translateY(-2px); box-shadow: 0 6px 16px rgba(74,159,232,.18); text-decoration: none; }
.uc-quick .uq-ico { font-size: 24px; line-height: 1; }
.uc-quick b { color: var(--blue-deep); font-size: 15px; }
.uc-quick i { font-style: normal; color: #999; font-size: 12.5px; }

/* 锁定答案按钮 */
.answer-btn.locked {
  background: #eee; color: #999; border: 1px solid #ddd; cursor: not-allowed;
  box-shadow: none; transform: none;
}
.answer-btn.locked:hover { background: #eee; color: #999; transform: none; box-shadow: none; }

/* 表单 */
.f-label { display: block; font-size: 13px; color: #555; margin: 12px 0 4px; }
.f-input {
  width: 100%; box-sizing: border-box; padding: 10px 12px;
  border: 1px solid #ccd9e5; border-radius: 8px; font-size: 14px; font-family: inherit;
}
.f-input:focus { outline: none; border-color: var(--blue-main); box-shadow: 0 0 0 3px rgba(74,159,232,.15); }
.f-btn {
  width: 100%; margin-top: 18px; padding: 12px; border: none; border-radius: 8px;
  background: linear-gradient(135deg, var(--blue-main), #7FC4F5); color: #fff;
  font-size: 15px; font-weight: 700; cursor: pointer; transition: all .2s;
}
.f-btn:hover { transform: translateY(-1px); box-shadow: 0 4px 12px rgba(74,159,232,.3); }
.form-tip { margin-bottom: 14px; }

/* VIP 套餐 */
.vip-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(220px, 1fr)); gap: 16px; margin-top: 18px; }
.vip-card {
  background: #fff; border: 2px solid var(--border); border-radius: 14px; text-align: center;
  padding: 22px 16px; transition: all .25s; display: flex; flex-direction: column; align-items: center;
}
.vip-card:hover { border-color: var(--blue-main); transform: translateY(-3px); box-shadow: 0 8px 20px rgba(74,159,232,.15); }
.vip-name { font-size: 15px; font-weight: 700; color: #333; }
.vip-price { margin: 8px 0 2px; font-size: 15px; color: #d98324; }
.vip-price b { font-size: 34px; }
.vip-days { color: #999; font-size: 13px; margin-bottom: 8px; }
.vip-desc { color: #888; font-size: 12px; min-height: 34px; margin-bottom: 14px; }
.vip-buy {
  display: inline-block; padding: 9px 28px; border-radius: 22px;
  background: linear-gradient(135deg, #f6c453, #f0a32c); color: #fff; font-weight: 700; font-size: 14px;
  transition: all .2s;
}
.vip-buy:hover { transform: translateY(-1px); box-shadow: 0 4px 12px rgba(240,163,44,.4); }

/* 信息表格 */
.info-table { width: 100%; border-collapse: collapse; font-size: 14px; }
.info-table th, .info-table td { padding: 9px 12px; border-bottom: 1px solid var(--border); text-align: left; }
.info-table th { color: #666; width: 110px; white-space: nowrap; background: var(--blue-bg); }
.info-table tr:last-child th, .info-table tr:last-child td { border-bottom: none; }

/* 支付轮询 */
.pay-spinner {
  display: inline-block; width: 14px; height: 14px; margin-right: 6px;
  border: 2px solid #ddd; border-top-color: var(--blue-main); border-radius: 50%;
  vertical-align: -2px; animation: spin 0.9s linear infinite;
}
@keyframes spin { to { transform: rotate(360deg); } }