/* Base layout and typography */
:root {
  --bg-1: #f6f1e7;
  --bg-2: #eef6ff;
  --ink: #1b1a17;
  --muted: #5b5a57;
  --accent: #d8672b;
  --accent-2: #1b7c7a;
  --card: #ffffff;
  --border: #e3d8c8;
  --shadow: 0 12px 30px rgba(30, 25, 20, 0.12);
  --code-bg: #f3f4f6;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  color: var(--ink);
  font-family: "Noto Serif SC", "Source Han Serif SC", "Songti SC", serif;
  background:
    radial-gradient(1200px 600px at 10% -20%, #fff4da 0%, transparent 60%),
    radial-gradient(900px 500px at 90% 0%, #e0f2ff 0%, transparent 55%),
    linear-gradient(180deg, var(--bg-1), var(--bg-2));
}

a {
  color: var(--accent-2);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

.container {
  width: min(980px, 92vw);
  margin: 0 auto;
}

.site-header {
  padding: 28px 0 18px;
  border-bottom: 1px solid var(--border);
  backdrop-filter: blur(4px);
}

.brand {
  font-family: "ZCOOL XiaoWei", "KaiTi", "STKaiti", serif;
  font-size: 28px;
  font-weight: 700;
  letter-spacing: 0.5px;
  color: var(--ink);
}

.subtitle {
  display: block;
  margin-top: 6px;
  color: var(--muted);
  font-size: 14px;
}

.lesson-nav {
  display: flex;
  gap: 14px;
  padding: 18px 0 6px;
  font-size: 14px;
}

.lesson-nav a {
  padding: 6px 12px;
  border-radius: 999px;
  border: 1px solid var(--border);
  background: rgba(255, 255, 255, 0.7);
}

.content {
  padding: 18px 0 40px;
  animation: fade-in 0.45s ease-out;
}

.content-card {
  padding: 26px;
  background: var(--card);
  border-radius: 18px;
  box-shadow: var(--shadow);
  border: 1px solid var(--border);
}

h1, h2, h3 {
  font-family: "ZCOOL XiaoWei", "KaiTi", "STKaiti", serif;
  letter-spacing: 0.4px;
}

h1 {
  font-size: 30px;
  margin: 0 0 12px;
}

h2 {
  margin-top: 24px;
  font-size: 22px;
}

h3 {
  margin-top: 18px;
  font-size: 18px;
}

p {
  line-height: 1.8;
  margin: 12px 0;
}

ul, ol {
  line-height: 1.8;
  padding-left: 22px;
}

code {
  background: var(--code-bg);
  padding: 2px 6px;
  border-radius: 6px;
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
  font-size: 0.95em;
}

pre {
  background: var(--code-bg);
  padding: 14px 16px;
  border-radius: 10px;
  overflow: auto;
}

pre code {
  background: transparent;
  padding: 0;
}

blockquote {
  margin: 16px 0;
  padding: 12px 16px;
  border-left: 4px solid var(--accent);
  background: rgba(216, 103, 43, 0.08);
  border-radius: 8px;
}

.lesson-meta {
  margin-bottom: 14px;
  font-size: 14px;
  color: var(--muted);
}

.tag {
  display: inline-block;
  margin-left: 8px;
  padding: 2px 8px;
  border-radius: 999px;
  background: rgba(27, 124, 122, 0.12);
  color: var(--accent-2);
  font-size: 12px;
}

.content-body img {
  max-width: 100%;
  border-radius: 12px;
  margin: 12px 0;
  box-shadow: 0 10px 20px rgba(25, 25, 25, 0.12);
}

.index-list {
  display: grid;
  gap: 12px;
  margin-top: 18px;
}

.index-item {
  padding: 14px 16px;
  border-radius: 14px;
  border: 1px solid var(--border);
  background: rgba(255, 255, 255, 0.82);
}

.index-item span {
  color: var(--muted);
  font-size: 13px;
}

.site-footer {
  padding: 26px 0 40px;
  color: var(--muted);
  font-size: 13px;
}

@keyframes fade-in {
  from {
    opacity: 0;
    transform: translateY(8px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@media (max-width: 680px) {
  .lesson-nav {
    flex-wrap: wrap;
  }

  .content-card {
    padding: 18px;
  }
}
/* Sidebar layout */
.layout {
  display: flex;
  gap: 24px;
  align-items: flex-start;
}
.sidebar {
  position: sticky;
  top: 18px;
  width: 240px;
  padding: 18px 16px;
  background: rgba(255, 255, 255, 0.85);
  border: 1px solid var(--border);
  border-radius: 16px;
  box-shadow: var(--shadow);
}
.sidebar-title {
  font-family: "ZCOOL XiaoWei", "KaiTi", "STKaiti", serif;
  font-size: 18px;
  margin-bottom: 12px;
}
.sidebar-nav {
  display: grid;
  gap: 6px;
  font-size: 14px;
}
.sidebar-nav a {
  display: block;
  padding: 6px 10px;
  border-radius: 10px;
  color: var(--ink);
  background: rgba(255, 255, 255, 0.7);
  border: 1px solid transparent;
}
.sidebar-nav a:hover {
  border-color: var(--border);
  text-decoration: none;
}
.sidebar-nav a.active {
  background: var(--accent);
  color: #fff;
  border-color: rgba(0, 0, 0, 0.05);
}
.main {
  flex: 1;
  min-width: 0;
}
@media (max-width: 980px) {
  .layout {
    flex-direction: column;
  }
  .sidebar {
    position: static;
    width: 100%;
  }
  .sidebar-nav {
    grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
  }
}
/* Layout alignment override */
.layout {
  width: min(1180px, 94vw);
  margin: 0 auto;
}