/* ===========================
   1. 基础变量与重置
   =========================== */
:root {
  --bg: #fff; --text: #222; --muted: #666; --border: #ddd;
  --code: #f6f8fa; --link: #0366d6; --link-hover: #0056b3;
  --card-bg: #fff;
}

/* 自动适配系统深色模式 */
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0d1117; --text: #c9d1d9; --muted: #8b949e;
    --border: #30363d; --code: #161b22; --link: #58a6ff; --link-hover: #79c0ff;
    --card-bg: #161b22;
  }
}

html {
  /* 仅保留平滑滚动，不设置全局 padding，避免首页顶部空白 */
  scroll-behavior: smooth;
}

* { box-sizing: border-box; max-width: 100vw; }

body {
  margin: 0; font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  background: var(--bg); color: var(--text); line-height: 1.7;
  overflow-x: hidden;
}

a { text-decoration: none; color: var(--link); transition: color 0.2s; }
a:hover { color: var(--link-hover); }

/* ===========================
   2. 导航栏与公共布局
   ========================== */
.topbar {
  display: flex; justify-content: space-between; align-items: center;
  padding: 0.8rem 1.5rem; border-bottom: 1px solid var(--border);
  position: sticky; top: 0; background: var(--bg); z-index: 100;
  /* 增加毛玻璃质感，避免完全死白 */
  background: rgba(255, 255, 255, 0.95);
  backdrop-filter: blur(10px);
}
@media (prefers-color-scheme: dark) {
  .topbar { background: rgba(13, 17, 23, 0.95); }
}

.layout {
  display: flex; max-width: 1100px; margin: 0 auto; padding: 2rem; gap: 3rem;
}

.content { flex: 1; min-width: 0; }

/* ★★★ 核心修复：精准定位文章标题，防止被导航栏遮挡 ★★★ */
.content h2, 
.content h3 {
  scroll-margin-top: 6rem;
}

/* ===========================
   3. 按钮与页脚样式 (本次恢复)
   ========================== */
.article-footer {
  margin-top: 4rem;
  padding-top: 2rem;
  border-top: 1px solid var(--border);
}

/* 恢复“返回文章列表”的按钮样式 */
.back-btn {
  display: inline-block;
  padding: 0.6rem 1.2rem;
  border: 1px solid var(--border);
  border-radius: 6px;
  background: var(--bg);
  color: var(--text);
  font-size: 0.95rem;
  transition: all 0.2s;
  text-decoration: none; /* 防止下划线 */
}

.back-btn:hover {
  border-color: var(--link);
  color: var(--link);
  box-shadow: 0 4px 12px rgba(0,0,0,0.08);
  transform: translateY(-1px);
}

/* ===========================
   4. 首页样式 (保持之前修复)
   ========================== */
.index-wrap {
  max-width: 800px;
  margin: 0 auto;
  padding: 2rem 1.5rem;
}

.search-box {
  width: 100%;
  padding: 12px 16px;
  margin-bottom: 2rem;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--bg);
  color: var(--text);
  font-size: 1rem;
  transition: all 0.2s;
}
.search-box:focus {
  outline: none;
  border-color: var(--link);
  box-shadow: 0 0 0 3px rgba(3, 102, 214, 0.1);
}

.card {
  display: block;
  padding: 1.5rem;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--card-bg);
  transition: transform 0.2s, box-shadow 0.2s, border-color 0.2s;
}
.card:hover {
  transform: translateY(-2px);
  box-shadow: 0 8px 20px rgba(0,0,0,0.08);
  border-color: var(--link);
}
.card h2 {
  margin: 0 0 0.5rem 0;
  font-size: 1.4rem;
  color: var(--text);
}
.card .meta {
  font-size: 0.9rem;
  color: var(--muted);
}

/* ===========================
   5. 目录逻辑
   ========================== */
.toc {
  width: 240px; position: sticky; top: 5.5rem;
  height: fit-content; max-height: calc(100vh - 7rem);
  overflow-y: auto; font-size: 0.95rem;
}

.toc-header {
  display: flex; justify-content: space-between; align-items: center;
  margin-bottom: 1rem; border-bottom: 1px solid var(--border); padding-bottom: 0.5rem;
}

.toc ul { list-style: none; padding: 0; margin: 0; }
.toc li { margin: 0.6rem 0; }
.toc li.h3 { padding-left: 1.2rem; font-size: 0.85em; }
.toc a { color: var(--muted); display: block; line-height: 1.4; }
.toc a:hover { color: var(--link); }

/* 目录按钮（移动端） */
.toc-btn {
  display: none; background: none; border: 1px solid var(--border);
  padding: 4px 10px; border-radius: 4px; color: var(--text); cursor: pointer;
}

@media (min-width: 769px) {
  .toc-close { display: none !important; }
}

/* ===========================
   6. 响应式与媒体适配
   ========================== */
@media (max-width: 768px) {
  .layout { flex-direction: column; padding: 1.2rem; }
  .toc {
    position: fixed; top: 0; right: -300px;
    width: 280px; height: 100%;
    background: var(--bg); box-shadow: -5px 0 15px rgba(0,0,0,0.1);
    z-index: 1001; transition: right 0.3s ease; padding: 1.5rem;
  }
  .toc.open { right: 0; }
  .toc-btn { display: block; }
  .toc-close { background: none; border: none; font-size: 1.5rem; color: var(--text); cursor: pointer; }
}

video, img { max-width: 100%; height: auto; border-radius: 4px; }
video { margin: 1.5rem 0; border-radius: 8px; }