/* ==========================================================================
   同余探索（Modulo Explorer）核心设计系统样式
   ========================================================================== */

:root {
  /* 基础色彩系统 (HSL) */
  --bg-primary: #0f172a;
  --bg-secondary: #1e293b;
  --bg-tertiary: #334155;
  --bg-card: rgba(30, 41, 59, 0.85);
  --bg-card-hover: rgba(51, 65, 85, 0.9);
  --border-color: rgba(255, 255, 255, 0.1);
  --border-focus: #38bdf8;
  
  --text-primary: #f8fafc;
  --text-secondary: #cbd5e1;
  --text-muted: #94a3b8;
  
  --accent-primary: #38bdf8;       /* 天蓝：主交互与高亮 */
  --accent-secondary: #818cf8;     /* 靛蓝：姐姐导师色 */
  --accent-younger: #34d399;       /* 翡翠绿：妹妹探索色 */
  --accent-gold: #fbbf24;          /* 琥珀金：重点技巧与星标 */
  --accent-crimson: #f43f5e;       /* 绯红：错误与易错警告 */
  
  /* 四色概念卡片系统 */
  --concept-green-bg: rgba(16, 185, 129, 0.12);
  --concept-green-border: #10b981;
  --concept-green-text: #6ee7b7;
  
  --concept-blue-bg: rgba(56, 189, 248, 0.12);
  --concept-blue-border: #0284c7;
  --concept-blue-text: #7dd3fc;
  
  --concept-orange-bg: rgba(245, 158, 11, 0.12);
  --concept-orange-border: #f59e0b;
  --concept-orange-text: #fcd34d;
  
  --concept-gray-bg: rgba(100, 116, 139, 0.12);
  --concept-gray-border: #64748b;
  --concept-gray-text: #cbd5e1;
  
  /* 字体系统 */
  --font-sans: 'Noto Sans SC', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  --font-serif: 'Noto Serif SC', Georgia, serif;
  --font-mono: 'Fira Code', Consolas, monospace;
  
  /* 布局与间距 */
  --header-height: 64px;
  --sidebar-width: 290px;
  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 20px;
  --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.2);
  --shadow-md: 0 8px 24px rgba(0, 0, 0, 0.3);
  --shadow-lg: 0 16px 40px rgba(0, 0, 0, 0.45);
}

/* 浅色主题覆盖 */
[data-theme="light"] {
  --bg-primary: #f8fafc;
  --bg-secondary: #ffffff;
  --bg-tertiary: #f1f5f9;
  --bg-card: rgba(255, 255, 255, 0.92);
  --bg-card-hover: #ffffff;
  --border-color: rgba(0, 0, 0, 0.08);
  --border-focus: #0284c7;
  
  --text-primary: #0f172a;
  --text-secondary: #334155;
  --text-muted: #64748b;
  
  --concept-green-bg: #ecfdf5;
  --concept-green-text: #065f46;
  --concept-blue-bg: #f0f9ff;
  --concept-blue-text: #0369a1;
  --concept-orange-bg: #fffbeb;
  --concept-orange-text: #92400e;
  --concept-gray-bg: #f8fafc;
  --concept-gray-text: #334155;
}

/* 全局重置与基础设定 */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  font-size: 16px;
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-sans);
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.7;
  min-height: 100vh;
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* 应用骨架 */
.app-container {
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

/* 顶部导航 */
.app-header {
  position: sticky;
  top: 0;
  z-index: 100;
  height: var(--header-height);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 24px;
  background: var(--bg-secondary);
  border-bottom: 1px solid var(--border-color);
  backdrop-filter: blur(12px);
}

.header-left {
  display: flex;
  align-items: center;
  gap: 14px;
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
}

.brand-badge {
  background: linear-gradient(135deg, #0284c7, #6366f1);
  color: #fff;
  font-size: 0.72rem;
  font-weight: 900;
  letter-spacing: 0.08em;
  padding: 3px 8px;
  border-radius: 6px;
  font-family: var(--font-mono);
}

.brand-title {
  font-size: 1.05rem;
  font-weight: 700;
  color: var(--text-primary);
  letter-spacing: -0.01em;
}

.header-center {
  display: flex;
  align-items: center;
}

.chapter-indicator {
  font-size: 0.92rem;
  font-weight: 600;
  color: var(--accent-primary);
  background: rgba(56, 189, 248, 0.1);
  padding: 5px 14px;
  border-radius: 20px;
  border: 1px solid rgba(56, 189, 248, 0.2);
}

.header-right {
  display: flex;
  align-items: center;
  gap: 16px;
}

.progress-bar-mini {
  width: 100px;
  height: 8px;
  background: var(--bg-tertiary);
  border-radius: 4px;
  overflow: hidden;
}

.progress-fill {
  height: 100%;
  background: linear-gradient(90deg, #38bdf8, #818cf8);
  transition: width 0.4s ease;
}

.progress-label {
  font-size: 0.82rem;
  font-family: var(--font-mono);
  color: var(--text-muted);
}

.icon-btn {
  background: transparent;
  border: 1px solid var(--border-color);
  color: var(--text-secondary);
  border-radius: var(--radius-sm);
  width: 36px;
  height: 36px;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: all 0.2s ease;
}

.icon-btn:hover {
  background: var(--bg-tertiary);
  color: var(--text-primary);
  border-color: var(--border-focus);
}

/* 主体布局 */
.main-layout {
  display: flex;
  flex: 1;
  position: relative;
}

/* 侧边栏 */
.sidebar {
  width: var(--sidebar-width);
  background: var(--bg-secondary);
  border-right: 1px solid var(--border-color);
  height: calc(100vh - var(--header-height));
  position: sticky;
  top: var(--header-height);
  overflow-y: auto;
  padding: 20px 16px;
  display: flex;
  flex-direction: column;
  gap: 16px;
  transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  z-index: 90;
}

.sidebar-header h3 {
  font-size: 1rem;
  font-weight: 700;
  color: var(--text-primary);
}

.sidebar-subtitle {
  font-size: 0.8rem;
  color: var(--text-muted);
}

.chapter-nav-list {
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.nav-volume-group {
  margin-top: 14px;
}

.nav-volume-title {
  font-size: 0.76rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--text-muted);
  padding: 6px 10px;
  margin-bottom: 4px;
}

.nav-item {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 9px 12px;
  border-radius: var(--radius-sm);
  color: var(--text-secondary);
  text-decoration: none;
  font-size: 0.88rem;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.2s ease;
  border: 1px solid transparent;
}

.nav-item:hover {
  background: var(--bg-tertiary);
  color: var(--text-primary);
}

.nav-item.active {
  background: rgba(56, 189, 248, 0.15);
  color: var(--accent-primary);
  font-weight: 700;
  border-color: rgba(56, 189, 248, 0.3);
}

.nav-item-num {
  font-family: var(--font-mono);
  font-size: 0.78rem;
  font-weight: 700;
  padding: 2px 6px;
  background: var(--bg-tertiary);
  border-radius: 4px;
}

.nav-item.active .nav-item-num {
  background: var(--accent-primary);
  color: #0f172a;
}

/* 核心视口 */
.content-viewport {
  flex: 1;
  max-width: 960px;
  margin: 0 auto;
  padding: 32px 28px 100px;
  width: 100%;
}

/* 章节头部横幅 */
.section-banner {
  margin-bottom: 32px;
  padding-bottom: 20px;
  border-bottom: 1px solid var(--border-color);
}

.volume-badge {
  display: inline-block;
  font-size: 0.78rem;
  font-weight: 700;
  letter-spacing: 0.05em;
  color: var(--accent-secondary);
  background: rgba(129, 140, 248, 0.12);
  padding: 4px 10px;
  border-radius: 6px;
  margin-bottom: 12px;
}

.sec-title {
  font-size: 1.85rem;
  font-weight: 800;
  color: var(--text-primary);
  letter-spacing: -0.02em;
  margin-bottom: 8px;
  line-height: 1.3;
}

.sec-subtitle {
  font-size: 1.05rem;
  color: var(--text-secondary);
  font-weight: 400;
}

/* Blocks 容器 */
.blocks-container {
  display: flex;
  flex-direction: column;
  gap: 24px;
}

/* 底部行动栏 */
.interaction-footer {
  position: fixed;
  bottom: 0;
  left: var(--sidebar-width);
  right: 0;
  height: 72px;
  background: var(--bg-secondary);
  border-top: 1px solid var(--border-color);
  backdrop-filter: blur(12px);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 32px;
  z-index: 80;
  transition: left 0.3s ease;
}

.sidebar-collapsed .interaction-footer {
  left: 0;
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 20px;
  border-radius: var(--radius-sm);
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  border: 1px solid transparent;
  transition: all 0.2s ease;
}

.btn-primary {
  background: linear-gradient(135deg, #0284c7, #38bdf8);
  color: #0f172a;
  box-shadow: 0 4px 14px rgba(56, 189, 248, 0.35);
}

.btn-primary:hover {
  transform: translateY(-1px);
  box-shadow: 0 6px 20px rgba(56, 189, 248, 0.45);
}

.btn-secondary {
  background: var(--bg-tertiary);
  color: var(--text-primary);
  border-color: var(--border-color);
}

.btn-secondary:hover {
  background: var(--bg-card-hover);
  border-color: var(--border-focus);
}

.btn-pulse {
  animation: pulse-glow 2s infinite;
}

@keyframes pulse-glow {
  0% {
    box-shadow: 0 0 0 0 rgba(56, 189, 248, 0.5);
  }
  70% {
    box-shadow: 0 0 0 10px rgba(56, 189, 248, 0);
  }
  100% {
    box-shadow: 0 0 0 0 rgba(56, 189, 248, 0);
  }
}

/* ==========================================================================
   MathType / KaTeX 渲染优化样式
   ========================================================================== */
.katex {
  font-size: 1.08em;
  text-rendering: auto;
}

.katex-display {
  margin: 1.2em 0;
  padding: 12px 18px;
  background: rgba(15, 23, 42, 0.6);
  border-radius: var(--radius-sm);
  border: 1px solid var(--border-color);
  overflow-x: auto;
  overflow-y: hidden;
}

[data-theme="light"] .katex-display {
  background: #f1f5f9;
}

/* 响应式调整 */
@media (max-width: 900px) {
  .sidebar {
    position: fixed;
    transform: translateX(-100%);
    box-shadow: var(--shadow-lg);
  }
  .sidebar.open {
    transform: translateX(0);
  }
  .sidebar-overlay {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.5);
    backdrop-filter: blur(4px);
    z-index: 85;
  }
  .sidebar-overlay.active {
    display: block;
  }
  .interaction-footer {
    left: 0;
    padding: 0 16px;
  }
  .content-viewport {
    padding: 20px 16px 90px;
  }
}