:root {
    /* 颜色变量 */
    --color-deep-green: #1a472a;
    --color-deep-purple: #4b0082;
    --color-black: #333333;
    --color-white: #ffffff;
    --max-width: 1200px;
}

/* 基础样式重置 */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: Arial, sans-serif;
    line-height: 1.6;
    color: var(--color-black);
}

/* 头部样式 */
.site-header {
    background-color: #15214b;
    padding: 1rem 2rem;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

.header-container {
    max-width: 1200px;
    margin: 0 auto;
}

.site-title {
    font-size: 2rem;
    font-weight: 700;
    color: #ffffff;
    margin: 0;
    display: flex;
    align-items: center;
}

.domain-extension {
    color: #9eff66;
    font-weight: 500;
}

/* 响应式调整 */
@media (max-width: 768px) {
    .site-header {
        padding: 0.8rem 1rem;
    }
    
    .site-title {
        font-size: 1.5rem;
    }
}

/* 面包屑导航样式 */
.breadcrumb {
    max-width: var(--max-width);
    margin: 1rem auto;
    padding: 0 1rem;
}

.breadcrumb ol {
    list-style: none;
    display: flex;
    gap: 0.5rem;
}

.breadcrumb li:not(:last-child)::after {
    content: ">";
    margin-left: 0.5rem;
}

/* 主要内容区域样式 */
.main-content {
    max-width: var(--max-width);
    margin: 2rem auto;
    padding: 0 1rem;
}

.content-wrapper {
    display: grid;
    grid-template-columns: 3fr 1fr;
    gap: 2rem;
    align-items: start;
}

/* 标题样式 */
h2, h3, h4, h5, h6 {
    color: var(--color-deep-purple);
    margin-bottom: 1rem;
}

/* 侧边栏样式 */
.sidebar {
    position: sticky;
    top: 2rem;
    padding: 1rem;
    height: fit-content;
}

.sidebar h3 {
    color: var(--color-deep-purple);
}

.sidebar ul {
    list-style: none;
}

.sidebar li {
    margin-bottom: 0.5rem;
}

.sidebar a {
    color: var(--color-deep-purple);
    text-decoration: none;
}

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

/* 页脚样式 */
.site-footer {
    background-color: #f5f5f5;
    padding: 2rem 0;
    margin-top: 3rem;
}

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

.footer-nav ul {
    list-style: none;
    display: flex;
    gap: 2rem;
    margin-top: 1rem;
}

.footer-nav a {
    color: var(--color-black);
    text-decoration: none;
}

.footer-nav a:hover {
    text-decoration: underline;
}

/* 响应式设计 */
@media (max-width: 768px) {
    .content-wrapper {
        grid-template-columns: 1fr;
    }
    
    .header-container {
        flex-direction: column;
        text-align: center;
    }
    
    .footer-nav ul {
        flex-direction: column;
        gap: 1rem;
    }
}

.examples-content {
    padding: 2rem;
    background-color: #ffffff;
    border-radius: 8px;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

.level-indicator {
    margin-bottom: 1.5rem;
    color: #666;
    font-weight: 500;
}

.introduction {
    margin-bottom: 2rem;
}

.highlight {
    color: var(--color-deep-purple);
    font-weight: 500;
}

.tense-forms {
    width: 100%;
    margin: 2rem 0;
    border-collapse: collapse;
}

.tense-forms td {
    padding: 1rem;
    border: 1px solid #eee;
}

.tense-forms tr:nth-child(even) {
    background-color: #f9f9f9;
}

.example-box {
    background-color: #f8f9fa;
    padding: 1.5rem;
    margin: 1rem 0;
    border-left: 4px solid var(--color-deep-purple);
    border-radius: 4px;
}

.example-box p {
    margin-bottom: 0.8rem;
}

.example-box p:last-child {
    margin-bottom: 0;
}

.example-box i {
    color: var(--color-deep-purple);
    font-style: italic;
}

/* 练习题部分样式 */
.practice-section {
    margin-top: 3rem;
    border: 1px solid #eee;
    border-radius: 8px;
    overflow: hidden;
}

.practice-header {
    display: flex;
    border-bottom: 1px solid #eee;
}

.tab-button {
    padding: 1rem 2rem;
    border: none;
    background: none;
    cursor: pointer;
    font-size: 1rem;
    color: var(--color-black);
    flex: 1;
}

.tab-button.active {
    background-color: var(--color-deep-purple);
    color: var(--color-white);
}

.tab-content {
    display: none;
    padding: 2rem;
}

.tab-content.active {
    display: block;
}

.question-list,
.answer-list {
    list-style-position: inside;
    padding: 0;
}

.question-list li,
.answer-list li {
    margin-bottom: 1.5rem;
    line-height: 1.6;
}

.answer-list strong {
    color: var(--color-deep-purple);
}

.answer-list li {
    margin-bottom: 2rem;
    padding-bottom: 1rem;
    border-bottom: 1px solid #eee;
}

.answer-key {
    font-size: 1.2rem;
    margin-bottom: 0.5rem;
    color: var(--color-deep-purple);
}

.verb-answer {
    font-family: 'Courier New', monospace;
    font-weight: 700;
    font-size: 1.3rem;
    color: var(--color-deep-purple);
    background-color: #f0f0f0;
    padding: 0.2rem 0.5rem;
    border-radius: 4px;
}

.complete-sentence {
    font-size: 1.1rem;
    color: #444;
    margin-bottom: 0.8rem;
}

.explanation {
    color: #666;
    line-height: 1.8;
    margin-left: 1rem;
    font-size: 1rem;
}

.answer-list li:last-child {
    border-bottom: none;
    margin-bottom: 0;
}

/* 高级用法部分样式 */
.advanced-usage-section {
    margin: 3rem 0;
    padding: 2rem;
    background-color: #f8f9fa;
    border-radius: 8px;
    border-left: 4px solid var(--color-deep-purple);
}

.usage-category {
    margin: 2rem 0;
}

.usage-category h4 {
    color: var(--color-deep-purple);
    margin-bottom: 1rem;
    font-size: 1.1rem;
}

.example-box.narrative,
.example-box.summary {
    background-color: white;
    padding: 1.5rem;
    border-radius: 6px;
    box-shadow: 0 2px 4px rgba(0,0,0,0.05);
    margin: 1rem 0;
}

.example-box .highlight {
    color: var(--color-deep-purple);
    font-weight: 500;
    padding: 0 0.2rem;
}

.explanation {
    margin-top: 1rem;
    padding-top: 1rem;
    border-top: 1px solid #eee;
    font-size: 0.95rem;
    color: #666;
}

.explanation p {
    margin-bottom: 0.5rem;
}

/* 响应式调整 */
@media (max-width: 768px) {
    .advanced-usage-section {
        padding: 1rem;
        margin: 2rem 0;
    }
    
    .example-box.narrative,
    .example-box.summary {
        padding: 1rem;
    }
}

/* 完整故事答案样式 */
.complete-story-answer {
    background-color: #f8f9fa;
    padding: 2rem;
    border-radius: 8px;
    margin-bottom: 2rem;
    border-left: 4px solid var(--color-deep-purple);
}

.complete-story-answer h4 {
    color: var(--color-deep-purple);
    margin-bottom: 1rem;
}

.highlight-answer {
    color: var(--color-deep-purple);
    font-weight: 700;
    background-color: #e9ecef;
    padding: 0.2rem 0.4rem;
    border-radius: 4px;
}

.answer-explanations {
    margin-top: 2rem;
}

.answer-explanations h4 {
    color: var(--color-deep-purple);
    margin-bottom: 1.5rem;
}

.answer-key {
    font-weight: 700;
    color: var(--color-deep-purple);
    margin-bottom: 0.5rem;
}

.explanation {
    color: #666;
    margin-left: 1rem;
    margin-bottom: 1.5rem;
}

/* 响应式调整 */
@media (max-width: 768px) {
    .complete-story-answer {
        padding: 1rem;
    }
}

/* 目录导航样式 */
.table-of-contents {
    background-color: #f8f9fa;
    border-radius: 8px;
    padding: 1.5rem;
    margin: 2rem auto;
    max-width: var(--max-width);
    border: 1px solid #e9ecef;
    transition: all 0.3s ease;
}

.table-of-contents.sticky {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 1000;
    border-radius: 0;
    background-color: rgba(248, 249, 250, 0.95);
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
    padding: 0.5rem;
    margin: 0;
}

.table-of-contents.sticky .toc-list {
    max-height: 0;
    overflow: hidden;
}

.table-of-contents.sticky:hover .toc-list {
    max-height: 500px;
}

.toc-header {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    margin-bottom: 1rem;
}

.toc-icon {
    font-size: 1.2rem;
}

.toc-header h2 {
    margin: 0;
    font-size: 1.2rem;
    color: var(--color-deep-purple);
}

.toc-list {
    list-style: none;
    padding: 0;
    margin: 0;
    transition: max-height 0.3s ease;
}

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

.toc-list a {
    color: var(--color-deep-purple);
    text-decoration: none;
    display: block;
    padding: 0.3rem 0;
    transition: color 0.2s ease;
}

.toc-list a:hover {
    color: var(--color-deep-green);
}

/* 响应式调整 */
@media (max-width: 768px) {
    .table-of-contents {
        margin: 1rem;
        padding: 1rem;
    }
    
    .table-of-contents.sticky {
        padding: 0.5rem 1rem;
    }
}

/* 内容区域样式 */
.content-section {
    margin-bottom: 4rem;
    padding-top: 2rem;
}

.content-section h2 {
    color: var(--color-deep-purple);
    margin-bottom: 1.5rem;
    padding-bottom: 0.5rem;
    border-bottom: 2px solid var(--color-deep-purple);
}

/* 平滑滚动效果 */
html {
    scroll-behavior: smooth;
}

/* 为固定导航条预留空间 */
.content-section:first-child {
    padding-top: 0;
}

/* 响应式调整 */
@media (max-width: 768px) {
    .content-section {
        margin-bottom: 3rem;
        padding-top: 1.5rem;
    }
}

/* Introduction section styles */
.intro-content {
    max-width: 1200px;
    margin: 0 auto;
}

.section-intro {
    font-size: 1.2rem;
    line-height: 1.6;
    color: #2c3e50;
    margin-bottom: 2rem;
}

/* Key points box styles */
.key-points-box {
    background-color: #f8f9fa;
    border-radius: 8px;
    padding: 2rem;
    margin: 2rem 0;
    border-left: 4px solid var(--color-deep-purple);
}

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

.point-card {
    background: white;
    padding: 1.5rem;
    border-radius: 8px;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

.point-card h4 {
    color: var(--color-deep-purple);
    margin-bottom: 1rem;
}

.point-card ul {
    list-style: none;
    padding: 0;
}

.point-card li {
    margin-bottom: 0.5rem;
    padding-left: 1.5rem;
    position: relative;
}

.point-card li::before {
    content: "•";
    color: var(--color-deep-purple);
    position: absolute;
    left: 0;
}

/* Comparison table styles */
.comparison-table-wrapper {
    margin: 2rem 0;
    overflow-x: auto;
}

.comparison-table {
    width: 100%;
    border-collapse: collapse;
    margin-top: 1rem;
    background: white;
}

.comparison-table th,
.comparison-table td {
    padding: 1rem;
    text-align: left;
    border: 1px solid #e9ecef;
}

.comparison-table th {
    background-color: var(--color-deep-purple);
    color: white;
}

.comparison-table tr:nth-child(even) {
    background-color: #f8f9fa;
}

.comparison-table tr:hover {
    background-color: #e9ecef;
}

/* Responsive adjustments */
@media (max-width: 768px) {
    .points-grid {
        grid-template-columns: 1fr;
    }
    
    .comparison-table {
        font-size: 0.9rem;
    }
    
    .comparison-table th,
    .comparison-table td {
        padding: 0.75rem;
    }
}

/* Present Simple section styles */
.grammar-structure {
    background-color: #f8f9fa;
    padding: 2rem;
    border-radius: 8px;
    margin: 2rem 0;
}

.structure-box {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 2rem;
    margin-top: 1.5rem;
}

.structure-item {
    background: white;
    padding: 1.5rem;
    border-radius: 8px;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

.structure-item h4 {
    color: var(--color-deep-purple);
    margin-bottom: 1rem;
    padding-bottom: 0.5rem;
    border-bottom: 2px solid var(--color-deep-purple);
}

.formula {
    font-family: 'Courier New', monospace;
    background-color: #e9ecef;
    padding: 0.5rem 1rem;
    border-radius: 4px;
    margin: 1rem 0;
    font-weight: bold;
}

.note {
    color: #666;
    font-style: italic;
    margin: 0.5rem 0;
    font-size: 0.9rem;
}

.examples {
    margin-top: 1rem;
}

.examples p {
    margin: 0.5rem 0;
}

.highlight {
    color: var(--color-deep-purple);
    font-weight: bold;
    background-color: #f0f0f0;
    padding: 0.2rem 0.4rem;
    border-radius: 4px;
}

/* Usage section styles */
.usage-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 2rem;
    margin: 2rem 0;
}

.usage-card {
    background: white;
    padding: 1.5rem;
    border-radius: 8px;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
    border-top: 4px solid var(--color-deep-purple);
}

.usage-card h4 {
    color: var(--color-deep-purple);
    margin-bottom: 1rem;
}

.example-box {
    background-color: #f8f9fa;
    padding: 1rem;
    border-radius: 6px;
    margin-top: 1rem;
}

.example-box p {
    margin: 0.5rem 0;
}

/* Time expressions table styles */
.time-expressions {
    margin: 3rem 0;
}

.expression-table-wrapper {
    overflow-x: auto;
    margin-top: 1.5rem;
    background: white;
    border-radius: 8px;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

.expression-table {
    width: 100%;
    border-collapse: collapse;
}

.expression-table th,
.expression-table td {
    padding: 1rem;
    text-align: left;
    border: 1px solid #e9ecef;
}

.expression-table th {
    background-color: var(--color-deep-purple);
    color: white;
    font-weight: 500;
}

.expression-table tr:nth-child(even) {
    background-color: #f8f9fa;
}

.expression-table tr:hover {
    background-color: #e9ecef;
}

.expression-table td:first-child {
    font-weight: 500;
    color: var(--color-deep-purple);
}

/* Responsive adjustments */
@media (max-width: 768px) {
    .grammar-structure,
    .usage-card,
    .example-box {
        padding: 1rem;
    }

    .structure-box,
    .usage-grid {
        grid-template-columns: 1fr;
        gap: 1rem;
    }

    .expression-table {
        font-size: 0.9rem;
    }

    .expression-table th,
    .expression-table td {
        padding: 0.75rem;
    }
}

/* Animation for hover effects */
.usage-card,
.structure-item {
    transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.usage-card:hover,
.structure-item:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 8px rgba(0,0,0,0.1);
}

/* Common mistakes section styles */
.common-mistakes {
    background-color: #f8f9fa;
    padding: 2rem;
    border-radius: 8px;
    margin: 3rem 0;
}

.mistakes-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 2rem;
    margin-top: 1.5rem;
}

.mistake-card {
    background: white;
    padding: 1.5rem;
    border-radius: 8px;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

.mistake-card h4 {
    color: var(--color-deep-purple);
    margin: 1rem 0;
}

.mistake-card h4:first-child {
    color: #dc3545; /* Red for incorrect usage */
}

.mistake-card h4:nth-of-type(2) {
    color: #28a745; /* Green for correct usage */
}

.mistake-card .explanation {
    margin-top: 1rem;
    padding-top: 1rem;
    border-top: 1px solid #e9ecef;
    font-style: italic;
    color: #666;
}

/* Usage notes styles */
.usage-note {
    margin-top: 1rem;
    padding-top: 0.5rem;
    border-top: 1px dashed #dee2e6;
    font-size: 0.9rem;
    color: #666;
    font-style: italic;
}

/* Enhanced example box styles */
.example-box {
    position: relative;
    background-color: #f8f9fa;
    padding: 1.5rem;
    border-radius: 6px;
    margin-top: 1rem;
}

.example-box p {
    margin: 0.8rem 0;
    line-height: 1.6;
}

/* Time expressions enhancements */
.expression-table td:first-child {
    font-weight: 600;
    color: var(--color-deep-purple);
    width: 20%;
}

.expression-table td:nth-child(2) {
    color: #2c3e50;
    font-family: 'Courier New', monospace;
}

.expression-table td:last-child {
    font-style: italic;
    color: #666;
}

/* Hover effects for cards */
.mistake-card {
    transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.mistake-card:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 8px rgba(0,0,0,0.1);
}

/* Responsive design adjustments */
@media (max-width: 768px) {
    .mistakes-grid {
        grid-template-columns: 1fr;
        gap: 1rem;
    }

    .common-mistakes {
        padding: 1rem;
        margin: 2rem 0;
    }

    .mistake-card {
        padding: 1rem;
    }

    .usage-note {
        font-size: 0.85rem;
    }
}

/* Print styles */
@media print {
    .common-mistakes,
    .usage-section,
    .time-expressions {
        break-inside: avoid;
    }

    .highlight {
        color: var(--color-deep-purple) !important;
        background: none;
        padding: 0;
    }
}

/* Present Perfect specific styles */
.comparison-box {
    background-color: #f8f9fa;
    padding: 1.5rem;
    border-radius: 6px;
    margin-top: 1rem;
    border-left: 3px solid var(--color-deep-purple);
}

.comparison-box p {
    margin: 0.8rem 0;
    line-height: 1.6;
}

.comparison-box .correct {
    color: #2c3e50;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.comparison-box .explanation {
    margin-top: 1rem;
    padding-top: 1rem;
    border-top: 1px dashed #dee2e6;
    color: #666;
    font-style: italic;
}

/* Enhanced time expressions table */
.expression-table td em {
    color: var(--color-deep-purple);
    font-style: normal;
    font-weight: 600;
    background-color: #f0f0f0;
    padding: 0.2rem 0.4rem;
    border-radius: 4px;
}

/* Structure box enhancements */
.structure-item .formula {
    display: inline-block;
    position: relative;
    padding: 0.75rem 1.5rem;
    background: linear-gradient(45deg, #f8f9fa, #e9ecef);
    border-left: 4px solid var(--color-deep-purple);
}

.structure-item .formula::before {
    content: '→';
    position: absolute;
    left: -12px;
    color: var(--color-deep-purple);
    opacity: 0;
    transition: opacity 0.3s ease;
}

.structure-item:hover .formula::before {
    opacity: 1;
}

/* Usage card enhancements */
.usage-card {
    position: relative;
    overflow: hidden;
}

.usage-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 4px;
    background: linear-gradient(90deg, var(--color-deep-purple), var(--color-deep-green));
}

/* Example highlighting improvements */
.example-box .highlight {
    position: relative;
    display: inline-block;
}

.example-box .highlight::after {
    content: '';
    position: absolute;
    bottom: -2px;
    left: 0;
    width: 100%;
    height: 2px;
    background-color: var(--color-deep-purple);
    opacity: 0.3;
}

/* Time expressions enhancements */
.time-expressions {
    position: relative;
    padding: 2rem;
    background-color: #f8f9fa;
    border-radius: 8px;
    margin: 3rem 0;
}

.time-expressions::before {
    content: '⏰';
    position: absolute;
    top: -15px;
    left: 2rem;
    background: white;
    padding: 0.5rem;
    border-radius: 50%;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

/* Interactive elements */
.structure-item,
.usage-card,
.mistake-card {
    cursor: pointer;
    transition: all 0.3s ease;
}

.structure-item:hover,
.usage-card:hover,
.mistake-card:hover {
    transform: translateY(-3px);
    box-shadow: 0 6px 12px rgba(0,0,0,0.1);
}

/* Print optimization */
@media print {
    .comparison-box,
    .example-box,
    .time-expressions {
        break-inside: avoid;
    }
    
    .structure-item,
    .usage-card,
    .mistake-card {
        break-inside: avoid;
        box-shadow: none;
        border: 1px solid #ddd;
    }
}

/* Responsive design improvements */
@media (max-width: 768px) {
    .time-expressions {
        padding: 1.5rem;
    }
    
    .time-expressions::before {
        left: 50%;
        transform: translateX(-50%);
    }
    
    .comparison-box {
        padding: 1rem;
    }
    
    .structure-item .formula {
        font-size: 0.9rem;
        padding: 0.5rem 1rem;
    }
}

/* Dark mode support */
@media (prefers-color-scheme: dark) {
    .comparison-box,
    .example-box {
        background-color: rgba(255,255,255,0.05);
    }
    
    .time-expressions::before {
        background-color: var(--color-deep-purple);
        color: white;
    }
}

/* Present Perfect Continuous specific styles */

/* Comparison section styles */
.comparison-section {
    background-color: #f8f9fa;
    padding: 2rem;
    border-radius: 8px;
    margin: 3rem 0;
}

.comparison-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(350px, 1fr));
    gap: 2rem;
    margin-top: 1.5rem;
}

.comparison-card {
    background: white;
    padding: 1.5rem;
    border-radius: 8px;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

.example-pair {
    background-color: #f8f9fa;
    padding: 1.5rem;
    border-radius: 6px;
    margin-top: 1rem;
}

.example-pair p {
    margin: 0.8rem 0;
    padding-left: 1.5rem;
    position: relative;
}

.example-pair .continuous::before {
    content: "→";
    position: absolute;
    left: 0;
    color: var(--color-deep-purple);
}

.example-pair .simple::before {
    content: "→";
    position: absolute;
    left: 0;
    color: var(--color-deep-green);
}

.example-pair .explanation {
    margin-top: 1rem;
    padding-top: 1rem;
    border-top: 1px dashed #dee2e6;
    font-style: italic;
    color: #666;
}

/* Enhanced mistake card styles */
.mistake-card .incorrect {
    color: #dc3545;
    position: relative;
    padding-left: 1.8rem;
}

.mistake-card .correct {
    color: #28a745;
    position: relative;
    padding-left: 1.8rem;
}

.mistake-card .incorrect::before,
.mistake-card .correct::before {
    position: absolute;
    left: 0;
}

/* Visual enhancements for examples */
.example-box {
    border-left: 4px solid var(--color-deep-purple);
    transition: border-color 0.3s ease;
}

.example-box:hover {
    border-left-color: var(--color-deep-green);
}

/* Timeline visualization for continuous actions */
.usage-card .example-box::before {
    content: '';
    position: absolute;
    top: 0;
    left: -4px;
    height: 100%;
    width: 4px;
    background: linear-gradient(to bottom, var(--color-deep-purple), var(--color-deep-green));
    opacity: 0;
    transition: opacity 0.3s ease;
}

.usage-card .example-box:hover::before {
    opacity: 1;
}

/* Enhanced highlight effects */
.highlight {
    position: relative;
    z-index: 1;
}

.highlight::after {
    content: '';
    position: absolute;
    bottom: -2px;
    left: 0;
    width: 100%;
    height: 2px;
    background: linear-gradient(90deg, var(--color-deep-purple), var(--color-deep-green));
    transform: scaleX(0);
    transition: transform 0.3s ease;
    z-index: -1;
}

.highlight:hover::after {
    transform: scaleX(1);
}

/* Interactive elements */
.comparison-card {
    transition: transform 0.3s ease, box-shadow 0.3s ease;
    cursor: pointer;
}

.comparison-card:hover {
    transform: translateY(-3px);
    box-shadow: 0 4px 8px rgba(0,0,0,0.15);
}

/* Responsive adjustments */
@media (max-width: 768px) {
    .comparison-section {
        padding: 1rem;
    }

    .comparison-grid {
        grid-template-columns: 1fr;
        gap: 1rem;
    }

    .example-pair {
        padding: 1rem;
    }
}

/* Dark mode support */
@media (prefers-color-scheme: dark) {
    .comparison-section {
        background-color: rgba(255,255,255,0.05);
    }

    .comparison-card,
    .example-pair {
        background-color: rgba(255,255,255,0.1);
    }

    .example-pair .explanation {
        color: rgba(255,255,255,0.7);
    }
}

/* Print optimization */
@media print {
    .comparison-section,
    .comparison-card {
        break-inside: avoid;
    }

    .highlight::after {
        display: none;
    }

    .example-pair {
        border: 1px solid #ddd;
    }
}
/* Questions and Negatives specific styles */

/* Tense breakdown styles */
.tense-breakdown {
    display: grid;
    gap: 2rem;
    margin: 2rem 0;
}

.tense-card {
    background: white;
    border-radius: 12px;
    padding: 2rem;
    box-shadow: 0 2px 8px rgba(0,0,0,0.1);
    transition: transform 0.3s ease, box-shadow 0.3s ease;
}

.tense-card:hover {
    transform: translateY(-3px);
    box-shadow: 0 4px 12px rgba(0,0,0,0.15);
}

.tense-card h3 {
    color: var(--color-deep-purple);
    padding-bottom: 0.5rem;
    border-bottom: 2px solid var(--color-deep-purple);
    margin-bottom: 1.5rem;
}

/* Form grid layout */
.form-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 1.5rem;
}

.form-box {
    background-color: #f8f9fa;
    padding: 1.5rem;
    border-radius: 8px;
    border-left: 4px solid var(--color-deep-purple);
}

.formula-box {
    margin-top: 1rem;
}

.formula {
    font-family: 'Courier New', monospace;
    background: linear-gradient(45deg, #f1f3f5, #e9ecef);
    padding: 0.75rem 1rem;
    border-radius: 6px;
    font-weight: 500;
    color: var(--color-deep-purple);
    margin-bottom: 1rem;
}

/* Question words section */
.question-words-section {
    background-color: #f8f9fa;
    padding: 2rem;
    border-radius: 12px;
    margin: 3rem 0;
}

.question-words-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 1.5rem;
    margin-top: 1.5rem;
}

.word-card {
    background: white;
    padding: 1.5rem;
    border-radius: 8px;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
    transition: transform 0.2s ease;
}

.word-card:hover {
    transform: translateY(-2px);
}

.word-card h4 {
    color: var(--color-deep-purple);
    margin-bottom: 1rem;
    font-size: 1.2rem;
}

.word-card .example {
    margin: 0.5rem 0;
    color: #495057;
}

/* Tips section */
.tips-section {
    margin: 3rem 0;
}

.tips-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 2rem;
    margin-top: 1.5rem;
}

.tip-card {
    background: white;
    padding: 1.5rem;
    border-radius: 8px;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
    border-top: 4px solid var(--color-deep-green);
}

.tip-card h4 {
    color: var(--color-deep-green);
    margin-bottom: 1rem;
}

.example-box {
    background-color: #f8f9fa;
    padding: 1rem;
    border-radius: 6px;
    margin-top: 1rem;
}

/* Highlight animations */
.highlight {
    position: relative;
    display: inline-block;
    padding: 0 0.2rem;
}

.highlight::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: 100%;
    height: 2px;
    background: linear-gradient(90deg, var(--color-deep-purple), var(--color-deep-green));
    transform: scaleX(0);
    transition: transform 0.3s ease;
}

.highlight:hover::after {
    transform: scaleX(1);
}

/* Responsive adjustments */
@media (max-width: 768px) {
    .tense-card,
    .form-box,
    .word-card,
    .tip-card {
        padding: 1rem;
    }

    .question-words-section {
        padding: 1.5rem;
    }

    .formula {
        font-size: 0.9rem;
        padding: 0.5rem 0.75rem;
    }
}

/* Dark mode support */
@media (prefers-color-scheme: dark) {
    .tense-card,
    .word-card,
    .tip-card {
        background-color: rgba(255,255,255,0.05);
    }

    .form-box,
    .example-box {
        background-color: rgba(0,0,0,0.1);
    }

    .formula {
        background: linear-gradient(45deg, rgba(255,255,255,0.05), rgba(255,255,255,0.1));
    }
}

/* Print optimization */
@media print {
    .tense-card,
    .word-card,
    .tip-card {
        break-inside: avoid;
        box-shadow: none;
        border: 1px solid #ddd;
    }

    .highlight::after {
        display: none;
    }
}