/* Google Fonts - Noto Serif SC for a more elegant feel */
@import url('https://fonts.googleapis.com/css2?family=Noto+Serif+SC:wght@400;700&display=swap');

:root {
    --primary-color: #0d47a1; /* 深蓝色 */
    --secondary-color: #1565c0; /* 较亮的蓝色 */
    --text-color: #333;
    --bg-color: #f8f9fa;
    --content-bg: #ffffff;
    --border-color: #dee2e6;
}

body {
    font-family: 'Noto Serif SC', serif;
    line-height: 1.8;
    margin: 0;
    background-color: var(--bg-color);
    color: var(--text-color);
    font-size: 18px;
}

header {
    background: var(--primary-color);
    color: white;
    padding: 2rem 1rem;
    text-align: center;
    border-bottom: 5px solid var(--secondary-color);
}

header h1 {
    margin: 0;
    font-size: 2.5rem;
}

header p {
    margin: 0.5rem 0 0;
    font-style: italic;
    opacity: 0.9;
}

nav {
    background: var(--secondary-color);
    padding: 1rem;
    position: sticky;
    top: 0;
    z-index: 1000;
    box-shadow: 0 2px 5px rgba(0,0,0,0.1);
}

nav ul {
    list-style: none;
    padding: 0;
    margin: 0;
    display: flex;
    justify-content: center;
    flex-wrap: wrap; /* 在小屏幕上换行 */
}

nav ul li {
    margin: 5px 15px;
}

nav a {
    color: white;
    text-decoration: none;
    font-weight: bold;
    padding: 0.5rem 1rem;
    border-radius: 5px;
    transition: background-color 0.3s ease, color 0.3s ease;
}

nav a:hover, nav a.active {
    background-color: rgba(255, 255, 255, 0.2);
}

main {
    padding: 1rem;
}

.content-container {
    max-width: 900px;
    margin: 2rem auto;
    padding: 2rem 3rem;
    background: var(--content-bg);
    border-radius: 8px;
    box-shadow: 0 4px 12px rgba(0,0,0,0.08);
    border: 1px solid var(--border-color);
}

/* 章节内容样式 */
#content h1, #content h2, #content h3, #content h4 {
    color: var(--primary-color);
    border-bottom: 2px solid var(--border-color);
    padding-bottom: 0.5rem;
    margin-top: 2rem;
}

#content h1 { font-size: 2.2rem; }
#content h2 { font-size: 1.8rem; }
#content h3 { font-size: 1.5rem; }
#content h4 { font-size: 1.2rem; }

#content p, #content ul, #content ol {
    margin-bottom: 1.2rem;
}

#content strong {
    color: var(--secondary-color);
}

#content hr {
    border: 0;
    border-top: 2px solid var(--border-color);
    margin: 3rem 0;
}

#content table {
    width: 100%;
    border-collapse: collapse;
    margin: 2rem 0;
    font-size: 0.95em;
}

#content th, #content td {
    border: 1px solid var(--border-color);
    padding: 12px;
    text-align: left;
}

#content thead {
    background-color: #f2f2f2;
    font-weight: bold;
}

footer {
    text-align: center;
    padding: 2rem;
    margin-top: 40px;
    color: #777;
    font-size: 0.9em;
}

/* MathJax 样式调整 */
mjx-container {
    overflow-x: auto;
    overflow-y: hidden;
}

/* --- 新增的优化布局样式 --- */

/* 卡片式/高亮区域样式 */
.highlight-box, .definition-box, .theorem-box {
    margin: 2rem 0;
    padding: 1.5rem;
    border-left: 5px solid var(--primary-color);
    background-color: #f8f9fa; /* 使用主背景色或稍深的颜色 */
    border-radius: 0 8px 8px 0;
    box-shadow: 0 2px 8px rgba(0,0,0,0.05);
}

.highlight-box h3, .definition-box h3, .theorem-box h3 {
    margin-top: 0;
    color: var(--primary-color);
    font-size: 1.4rem;
    display: flex;
    align-items: center;
    border-bottom: none; /* 移除盒子内标题的下划线 */
}

/* 为不同类型的盒子添加不同的边框颜色 */
.definition-box {
    border-color: #28a745; /* 绿色 */
}
.definition-box h3 {
    color: #28a745;
}

.theorem-box {
    border-color: #dc3545; /* 红色 */
}
.theorem-box h3 {
    color: #dc3545;
}

/* 图标样式 (使用简单的emoji作为示例) */
.highlight-box h3::before, .definition-box h3::before, .theorem-box h3::before {
    margin-right: 0.75rem;
    font-size: 1.5rem;
    font-family: sans-serif; /* 确保emoji正确显示 */
}
.highlight-box h3::before { content: '💡'; } /* 重点 */
.definition-box h3::before { content: '📖'; } /* 定义 */
.theorem-box h3::before { content: '📜'; } /* 定理 */


/* 两栏布局 */
.two-column-layout {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 2rem;
    align-items: center;
    margin: 2rem 0;
}

/* 在小屏幕上变为单栏 */
@media (max-width: 768px) {
    .two-column-layout {
        grid-template-columns: 1fr;
    }
}

/* 交互式折叠区域 */
details {
    margin: 1.5rem 0;
    background: #fdfdfd;
    border: 1px solid var(--border-color);
    border-radius: 8px;
    transition: all 0.3s ease;
}
details[open] {
    box-shadow: 0 4px 12px rgba(0,0,0,0.08);
}
details summary {
    padding: 1rem 1.5rem;
    font-weight: bold;
    cursor: pointer;
    color: var(--secondary-color);
    outline: none;
    list-style-position: inside;
}
details summary:hover {
    background-color: #f2f2f2;
}
.details-content {
    padding: 0 1.5rem 1.5rem;
}

/* 公式容器 */
.formula-container {
    padding: 1.5rem;
    background-color: #e9ecef;
    border-radius: 8px;
    margin: 1.5rem 0;
    display: flex;
    justify-content: center;
    align-items: center;
    overflow-x: auto;
}