/* 基础变量和重置 */
:root {
    --color-primary: #15214b;
    --color-accent: #9eff66;
    --color-text: #333;
    --color-light-bg: #f8f9fa;
    --color-border: #e9ecef;
    --container-width: 1200px;
    --header-height: 70px;
    --sidebar-width: 280px;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    line-height: 1.6;
    color: var(--color-text);
    background-color: var(--color-light-bg);
}

.container {
    max-width: var(--container-width);
    margin: 0 auto;
    padding: 0 1rem;
}

/* Header 样式 */
.site-header {
    background-color: var(--color-primary);
    color: white;
    height: var(--header-height);
    display: flex;
    align-items: center;
}

.header-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    width: 100%;
}

.site-title {
    font-size: 1.8rem;
    font-weight: 700;
}

.domain-extension {
    color: var(--color-accent);
}

/* Welcome Section 样式 */
.welcome-section {
    padding: 4rem 0;
    text-align: center;
    background-color: white;
    border-bottom: 1px solid var(--color-border);
}

.welcome-section h2 {
    font-size: 2.5rem;
    margin-bottom: 1rem;
    color: var(--color-primary);
}

.welcome-section p {
    font-size: 1.2rem;
    color: #666;
    max-width: 600px;
    margin: 0 auto;
}

/* Navigation Grid 样式 */
.main-content {
    max-width: var(--container-width);
    margin: 0 auto;
    padding: 2rem 1rem;
}

.main-content .container {
    display: grid;
    grid-template-columns: 300px minmax(0, 1fr);
    gap: 2rem;
}

.tense-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 2rem;
    padding: 1rem 0;
}

.tense-card {
    background: white;
    border-radius: 8px;
    padding: 2rem;
    text-decoration: none;
    color: var(--color-text);
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
    transition: transform 0.3s ease, box-shadow 0.3s ease;
    border: 1px solid var(--color-border);
}

.tense-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 4px 8px rgba(0,0,0,0.15);
}

.tense-card h3 {
    font-size: 1.5rem;
    margin-bottom: 1rem;
    color: var(--color-primary);
}

.tense-card p {
    color: #666;
}

/* Footer 样式 */
.site-footer {
    background-color: var(--color-primary);
    color: white;
    padding: 2rem 0;
    margin-top: auto;
}

.site-footer p {
    text-align: center;
    font-size: 0.9rem;
    opacity: 0.8;
}

/* 响应式设计 */
@media (max-width: 768px) {
    .welcome-section {
        padding: 3rem 0;
    }

    .welcome-section h2 {
        font-size: 2rem;
    }

    .tense-grid {
        grid-template-columns: 1fr;
        gap: 1.5rem;
        padding: 1rem;
    }

    .tense-card {
        padding: 1.5rem;
    }
}

@media (max-width: 480px) {
    .site-title {
        font-size: 1.5rem;
    }

    .welcome-section h2 {
        font-size: 1.8rem;
    }

    .welcome-section p {
        font-size: 1rem;
    }
}

/* 面包屑导航样式 */
.breadcrumb {
    background-color: white;
    padding: 1rem 0;
    border-bottom: 1px solid var(--color-border);
}

.breadcrumb ul {
    list-style: none;
    display: flex;
    align-items: center;
}

.breadcrumb li {
    display: flex;
    align-items: center;
}

.breadcrumb li:not(:last-child)::after {
    content: "›";
    margin: 0 0.5rem;
    color: #666;
}

.breadcrumb a {
    color: var(--color-primary);
    text-decoration: none;
}

.breadcrumb a:hover {
    text-decoration: underline;
}

/* 侧边栏样式 */
.sidebar {
    position: sticky;
    top: 2rem;
    height: fit-content;
    background: white;
    border-radius: 8px;
    padding: 1.5rem;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

.outline-header h2 {
    font-size: 1.5rem;
    margin-bottom: 1rem;
    color: var(--color-primary);
}

.outline-list {
    list-style: none;
}

.outline-list ul {
    list-style: none;
    margin-left: 1.2rem;
    margin-top: 0.5rem;
}

.outline-list li {
    margin-bottom: 0.5rem;
}

.outline-list a {
    color: var(--color-text);
    text-decoration: none;
    font-size: 0.95rem;
    display: block;
    padding: 0.3rem 0;
}

.outline-list a:hover {
    color: var(--color-primary);
}

/* 文章内容样式 */
.main-article {
    background: white;
    border-radius: 8px;
    padding: 2rem;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
    min-width: 0;
}

.content-section {
    margin-bottom: 3rem;
}

.content-section h1 {
    font-size: 2.5rem;
    margin-bottom: 2rem;
    color: var(--color-primary);
}

.intro-section {
    margin-bottom: 2.5rem;
}

.intro-section h2 {
    font-size: 1.8rem;
    margin-bottom: 1rem;
    color: var(--color-primary);
}

.key-qualities {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 1.5rem;
    margin: 2rem 0;
}

.quality {
    background: var(--color-light-bg);
    padding: 1.5rem;
    border-radius: 8px;
}

.quality h3 {
    color: var(--color-primary);
    margin-bottom: 0.8rem;
}

/* Example Essays 样式 */
.example-essay {
    margin-bottom: 4rem;
    padding-bottom: 3rem;
    border-bottom: 1px solid var(--color-border);
}

.example-essay h2 {
    font-size: 2rem;
    margin-bottom: 1.5rem;
    color: var(--color-primary);
}

.essay-intro {
    font-size: 1.1rem;
    color: #666;
    margin-bottom: 1.5rem;
    font-style: italic;
}

.essay-body {
    margin-bottom: 2rem;
}

.essay-body p {
    margin-bottom: 1rem;
    line-height: 1.8;
}

.essay-analysis {
    background: var(--color-light-bg);
    padding: 1.5rem;
    border-radius: 8px;
}

.essay-analysis h3 {
    color: var(--color-primary);
    margin-bottom: 1.5rem;
}

.analysis-points {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 1.5rem;
}

.analysis-point h4 {
    color: var(--color-primary);
    margin-bottom: 0.5rem;
}

/* 响应式设计 */
@media (max-width: 1024px) {
    .main-content .container {
        grid-template-columns: 1fr;
    }

    .sidebar {
        position: static;
        margin-bottom: 2rem;
    }
}

@media (max-width: 768px) {
    .key-qualities {
        grid-template-columns: 1fr;
    }

    .analysis-points {
        grid-template-columns: 1fr;
    }

    .main-article {
        padding: 1.5rem;
    }

    .content-section h1 {
        font-size: 2rem;
    }
}

@media (max-width: 480px) {
    .example-essay h2 {
        font-size: 1.8rem;
    }

    .essay-intro {
        font-size: 1rem;
    }
}

/* Subject Areas Navigation 样式 */
.subject-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 1.5rem;
    margin-top: 2rem;
}

.subject-card {
    background: white;
    border-radius: 8px;
    padding: 1.5rem;
    text-decoration: none;
    color: var(--color-text);
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
    transition: transform 0.3s ease, box-shadow 0.3s ease;
    border: 1px solid var(--color-border);
}

.subject-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 4px 8px rgba(0,0,0,0.15);
    color: var(--color-primary);
}

.subject-card h3 {
    font-size: 1.3rem;
    margin-bottom: 0.8rem;
    color: var(--color-primary);
}

.subject-card p {
    font-size: 0.95rem;
    color: #666;
    line-height: 1.5;
}

/* 响应式调整 */
@media (max-width: 768px) {
    .subject-grid {
        grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
        gap: 1rem;
        margin-top: 1.5rem;
    }

    .subject-card {
        padding: 1.25rem;
    }
}

/* 侧边栏目录样式 */
.outline-nav {
    background: white;
    border-radius: 8px;
    padding: 1.5rem;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
    width: 300px;
}

.outline-header h2 {
    font-size: 1.5rem;
    margin-bottom: 1rem;
    color: var(--color-primary);
    font-weight: 700;
}

.outline-list {
    list-style: none;
}

/* 一级标题样式 (Introduction, Example Essays, Subject Areas) */
.outline-list > li > a {
    color: var(--color-primary);
    font-weight: 600;
    font-size: 1.1rem;
    padding: 0.3rem 0;
    display: block;
    margin-bottom: 0.3rem;
}

/* 二级标题样式 (What is..., Why Read..., 具体的essays) */
.outline-list ul li a {
    color: #555;
    font-size: 0.95rem;
    padding: 0.2rem 0;
    display: block;
    padding-left: 1rem;
    border-left: 2px solid transparent;
    transition: all 0.2s ease;
}

/* 悬停效果 */
.outline-list ul li a:hover {
    color: var(--color-primary);
    border-left-color: var(--color-primary);
    background-color: var(--color-light-bg);
    padding-left: 1.2rem;
}

/* 当前激活项样式 */
.outline-list ul li a.active {
    color: var(--color-primary);
    border-left-color: var(--color-primary);
    background-color: var(--color-light-bg);
    font-weight: 500;
}

/* 子列表间距 */
.outline-list ul {
    margin-left: 0.5rem;
    margin-bottom: 0.8rem;
}

/* 一级标题组之间的间距 */
.outline-list > li {
    margin-bottom: 1rem;
}

/* YouTube Video Container 样式 */
.video-container {
    position: relative;
    width: 100%;
    margin: 2rem 0;
    border-radius: 8px;
    overflow: hidden;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

.video-container iframe {
    display: block;
    border-radius: 8px;
}

/* 响应式视频容器 */
@media (max-width: 768px) {
    .video-container {
        margin: 1.5rem 0;
    }
    
    .video-container iframe {
        height: 300px;
    }
}

@media (max-width: 480px) {
    .video-container iframe {
        height: 240px;
    }
}
/* SEO Content Section 样式 */
.seo-content {
    margin-top: 4rem;
    padding-top: 2rem;
    border-top: 1px solid var(--color-border);
}

.seo-text {
    color: #666;
    font-size: 0.95rem;
    line-height: 1.6;
}

.seo-text h2 {
    color: var(--color-primary);
    font-size: 1.5rem;
    margin-bottom: 1.5rem;
}

.seo-text h3 {
    color: var(--color-primary);
    font-size: 1.2rem;
    margin: 1.5rem 0 1rem;
}

.seo-text p {
    margin-bottom: 1rem;
}

.seo-text ul, 
.seo-text ol {
    margin: 1rem 0;
    padding-left: 1.5rem;
}

.seo-text li {
    margin-bottom: 0.5rem;
}

.seo-tips {
    background: var(--color-light-bg);
    padding: 1.5rem;
    border-radius: 8px;
    margin: 2rem 0;
}

/* 响应式调整 */
@media (max-width: 768px) {
    .seo-content {
        margin-top: 3rem;
        padding-top: 1.5rem;
    }
    
    .seo-text h2 {
        font-size: 1.3rem;
    }
    
    .seo-text h3 {
        font-size: 1.1rem;
    }
}

/* 移动端导航样式 */
.nav-toggle {
    display: none;
    background: none;
    border: none;
    cursor: pointer;
    padding: 0.5rem;
}

.toggle-icon {
    display: block;
    width: 24px;
    height: 2px;
    background-color: var(--color-primary);
    position: relative;
    transition: all 0.3s ease;
}

.toggle-icon::before,
.toggle-icon::after {
    content: '';
    position: absolute;
    width: 24px;
    height: 2px;
    background-color: var(--color-primary);
    transition: all 0.3s ease;
}

.toggle-icon::before {
    top: -6px;
}

.toggle-icon::after {
    bottom: -6px;
}

/* 打开状态的图标样式 */
.nav-toggle.active .toggle-icon {
    background-color: transparent;
}

.nav-toggle.active .toggle-icon::before {
    transform: rotate(45deg);
    top: 0;
}

.nav-toggle.active .toggle-icon::after {
    transform: rotate(-45deg);
    bottom: 0;
}

@media (max-width: 768px) {
    .nav-toggle {
        display: block;
    }

    .outline-header {
        display: flex;
        justify-content: space-between;
        align-items: center;
    }

    .outline-content {
        max-height: 1000px;
        overflow: hidden;
        transition: max-height 0.3s ease-out;
    }

    .outline-content.collapsed {
        max-height: 0;
    }
}