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

:root {
    --primary-color: #2196F3;
    --secondary-color: #4CAF50;
    --accent-color: #FF9800;
    --danger-color: #F44336;
    --dark-color: #212121;
    --light-color: #F5F5F5;
    --white: #FFFFFF;
    --gray: #757575;
    --light-gray: #E0E0E0;
    --shadow: 0 2px 10px rgba(0,0,0,0.1);
    --border-radius: 8px;
    --transition: all 0.3s ease;
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    line-height: 1.6;
    color: var(--dark-color);
    background-color: var(--light-color);
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

/* Header Styles */
.header {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: var(--white);
    padding: 1rem 0;
    position: sticky;
    top: 0;
    z-index: 1000;
    box-shadow: var(--shadow);
}

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

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

.logo i {
    font-size: 2rem;
}

.logo h1 {
    font-size: 1.5rem;
    font-weight: 600;
}

.nav-list {
    display: flex;
    list-style: none;
    gap: 2rem;
}

.nav-link {
    color: var(--white);
    text-decoration: none;
    font-weight: 500;
    transition: var(--transition);
    padding: 0.5rem 1rem;
    border-radius: var(--border-radius);
}

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

.mobile-toggle {
    display: none;
    background: none;
    border: none;
    color: var(--white);
    font-size: 1.5rem;
    cursor: pointer;
}

/* Search Bar */
.search-container {
    background-color: var(--white);
    padding: 1rem 0;
    border-bottom: 1px solid var(--light-gray);
}

.search-box {
    position: relative;
    max-width: 600px;
    margin: 0 auto;
}

.search-box i {
    position: absolute;
    left: 15px;
    top: 50%;
    transform: translateY(-50%);
    color: var(--gray);
}

#search-input {
    width: 100%;
    padding: 12px 20px 12px 45px;
    border: 2px solid var(--light-gray);
    border-radius: 25px;
    font-size: 1rem;
    outline: none;
    transition: var(--transition);
}

#search-input:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(33, 150, 243, 0.1);
}

.search-results {
    position: absolute;
    top: 100%;
    left: 0;
    right: 0;
    background: var(--white);
    border: 1px solid var(--light-gray);
    border-radius: var(--border-radius);
    max-height: 300px;
    overflow-y: auto;
    z-index: 100;
    display: none;
}

.search-result-item {
    padding: 12px 20px;
    border-bottom: 1px solid var(--light-gray);
    cursor: pointer;
    transition: var(--transition);
}

.search-result-item:hover {
    background-color: var(--light-color);
}

/* Main Content */
.main {
    min-height: 80vh;
}

.section {
    display: none;
    padding: 2rem 0;
}

.section.active {
    display: block;
}

.section-header {
    text-align: center;
    margin-bottom: 3rem;
}

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

.section-header p {
    font-size: 1.2rem;
    color: var(--gray);
}

/* Hero Section */
.hero {
    text-align: center;
    padding: 3rem 0;
    background: linear-gradient(135deg, rgba(33, 150, 243, 0.1), rgba(76, 175, 80, 0.1));
    border-radius: var(--border-radius);
    margin-bottom: 3rem;
}

.hero h2 {
    font-size: 2.5rem;
    margin-bottom: 1rem;
    color: var(--dark-color);
}

.hero p {
    font-size: 1.2rem;
    color: var(--gray);
    margin-bottom: 2rem;
}

.hero-stats {
    display: flex;
    justify-content: center;
    gap: 3rem;
    flex-wrap: wrap;
}

.stat {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    color: var(--primary-color);
    font-weight: 600;
}

.stat i {
    font-size: 1.5rem;
}

/* Chapter Grid */
.chapter-overview h3 {
    text-align: center;
    font-size: 2rem;
    margin-bottom: 2rem;
    color: var(--dark-color);
}

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

.chapter-card {
    background: var(--white);
    padding: 2rem;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    transition: var(--transition);
    cursor: pointer;
    border: 2px solid transparent;
}

.chapter-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 4px 20px rgba(0,0,0,0.15);
    border-color: var(--primary-color);
}

.chapter-icon {
    text-align: center;
    margin-bottom: 1rem;
}

.chapter-icon i {
    font-size: 3rem;
    color: var(--primary-color);
}

.chapter-card h4 {
    font-size: 1.3rem;
    margin-bottom: 1rem;
    color: var(--dark-color);
}

.chapter-card p {
    color: var(--gray);
    margin-bottom: 1.5rem;
}

.progress-bar {
    width: 100%;
    height: 8px;
    background-color: var(--light-gray);
    border-radius: 4px;
    overflow: hidden;
}

.progress-fill {
    height: 100%;
    background: linear-gradient(90deg, var(--primary-color), var(--secondary-color));
    transition: width 0.3s ease;
}

/* Chapter Navigation */
.chapter-navigation {
    margin-bottom: 2rem;
}

.chapter-tabs {
    display: flex;
    gap: 0.5rem;
    overflow-x: auto;
    padding: 0.5rem;
    background-color: var(--white);
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
}

.chapter-tab {
    padding: 0.8rem 1.5rem;
    border: none;
    background-color: transparent;
    color: var(--gray);
    border-radius: var(--border-radius);
    cursor: pointer;
    transition: var(--transition);
    white-space: nowrap;
    font-weight: 500;
}

.chapter-tab.active,
.chapter-tab:hover {
    background-color: var(--primary-color);
    color: var(--white);
}

/* Chapter Content */
.chapter-content {
    background: var(--white);
    padding: 2rem;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    line-height: 1.8;
}

.chapter-content h3 {
    color: var(--primary-color);
    margin-bottom: 1rem;
    font-size: 1.8rem;
}

.chapter-content h4 {
    color: var(--dark-color);
    margin: 1.5rem 0 1rem 0;
    font-size: 1.4rem;
}

.chapter-content p {
    margin-bottom: 1rem;
    text-align: justify;
}

.chapter-content ul, .chapter-content ol {
    margin: 1rem 0 1rem 2rem;
}

.chapter-content li {
    margin-bottom: 0.5rem;
}

.concept-box {
    background: linear-gradient(135deg, rgba(33, 150, 243, 0.05), rgba(76, 175, 80, 0.05));
    border-left: 4px solid var(--primary-color);
    padding: 1.5rem;
    margin: 1.5rem 0;
    border-radius: 0 var(--border-radius) var(--border-radius) 0;
}

.concept-box h5 {
    color: var(--primary-color);
    margin-bottom: 0.5rem;
    font-size: 1.2rem;
}

/* Quiz Styles */
.quiz-type-selector {
    display: flex;
    gap: 1rem;
    margin-bottom: 2rem;
    justify-content: center;
}

.quiz-type-btn {
    padding: 1rem 2rem;
    border: 2px solid var(--primary-color);
    background: var(--white);
    color: var(--primary-color);
    border-radius: var(--border-radius);
    cursor: pointer;
    transition: var(--transition);
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-weight: 500;
}

.quiz-type-btn.active,
.quiz-type-btn:hover {
    background: var(--primary-color);
    color: var(--white);
}

.quiz-container {
    max-width: 800px;
    margin: 0 auto;
}

.question-card {
    background: var(--white);
    padding: 2rem;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    margin-bottom: 2rem;
}

.question-header {
    display: flex;
    justify-content: between;
    align-items: center;
    margin-bottom: 1.5rem;
}

.question-number {
    background: var(--primary-color);
    color: var(--white);
    padding: 0.5rem 1rem;
    border-radius: 50px;
    font-weight: 600;
}

.question-text {
    font-size: 1.2rem;
    margin-bottom: 1.5rem;
    color: var(--dark-color);
    line-height: 1.6;
}

.options {
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

.option {
    display: flex;
    align-items: center;
    padding: 1rem;
    border: 2px solid var(--light-gray);
    border-radius: var(--border-radius);
    cursor: pointer;
    transition: var(--transition);
}

.option:hover {
    border-color: var(--primary-color);
    background-color: rgba(33, 150, 243, 0.05);
}

.option input[type="radio"] {
    margin-right: 1rem;
    transform: scale(1.2);
}

.option.correct {
    border-color: var(--secondary-color);
    background-color: rgba(76, 175, 80, 0.1);
}

.option.incorrect {
    border-color: var(--danger-color);
    background-color: rgba(244, 67, 54, 0.1);
}

.explanation {
    margin-top: 1.5rem;
    padding: 1.5rem;
    background: linear-gradient(135deg, rgba(33, 150, 243, 0.05), rgba(76, 175, 80, 0.05));
    border-radius: var(--border-radius);
    border-left: 4px solid var(--primary-color);
    display: none;
}

.explanation.show {
    display: block;
    animation: fadeIn 0.3s ease;
}

.explanation h5 {
    color: var(--primary-color);
    margin-bottom: 0.5rem;
    font-size: 1.1rem;
}

.explanation p {
    line-height: 1.6;
    color: var(--dark-color);
}

/* Essay Question */
.essay-input {
    width: 100%;
    min-height: 120px;
    padding: 1rem;
    border: 2px solid var(--light-gray);
    border-radius: var(--border-radius);
    font-family: inherit;
    font-size: 1rem;
    resize: vertical;
    outline: none;
    transition: var(--transition);
}

.essay-input:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(33, 150, 243, 0.1);
}

/* Progress Dashboard */
.progress-dashboard {
    max-width: 1000px;
    margin: 0 auto;
}

.progress-stats {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 2rem;
    margin-bottom: 3rem;
}

.stat-card {
    background: var(--white);
    padding: 2rem;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    display: flex;
    align-items: center;
    gap: 1.5rem;
    transition: var(--transition);
}

.stat-card:hover {
    transform: translateY(-3px);
    box-shadow: 0 4px 20px rgba(0,0,0,0.15);
}

.stat-card i {
    font-size: 3rem;
    color: var(--primary-color);
}

.stat-info h3 {
    font-size: 2rem;
    color: var(--dark-color);
    margin-bottom: 0.5rem;
}

.stat-info p {
    color: var(--gray);
    font-size: 1.1rem;
}

.progress-detail {
    background: var(--white);
    padding: 2rem;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
}

.progress-detail h3 {
    margin-bottom: 2rem;
    color: var(--dark-color);
    font-size: 1.5rem;
}

/* Buttons */
.btn {
    padding: 0.8rem 2rem;
    border: none;
    border-radius: var(--border-radius);
    cursor: pointer;
    transition: var(--transition);
    font-weight: 500;
    text-decoration: none;
    display: inline-block;
    text-align: center;
}

.btn-primary {
    background: var(--primary-color);
    color: var(--white);
}

.btn-primary:hover {
    background: #1976D2;
    transform: translateY(-2px);
}

.btn-secondary {
    background: var(--secondary-color);
    color: var(--white);
}

.btn-secondary:hover {
    background: #388E3C;
    transform: translateY(-2px);
}

/* Footer */
.footer {
    background-color: var(--dark-color);
    color: var(--white);
    text-align: center;
    padding: 2rem 0;
    margin-top: 3rem;
}

/* Animations */
@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.fade-in {
    animation: fadeIn 0.5s ease;
}

/* Responsive Design */
@media (max-width: 768px) {
    .header .container {
        flex-wrap: wrap;
    }
    
    .nav-list {
        display: none;
        width: 100%;
        flex-direction: column;
        background-color: rgba(255, 255, 255, 0.1);
        border-radius: var(--border-radius);
        margin-top: 1rem;
        padding: 1rem;
    }
    
    .nav-list.active {
        display: flex;
    }
    
    .mobile-toggle {
        display: block;
    }
    
    .hero h2 {
        font-size: 2rem;
    }
    
    .hero-stats {
        gap: 1.5rem;
    }
    
    .section-header h2 {
        font-size: 2rem;
    }
    
    .chapter-grid {
        grid-template-columns: 1fr;
    }
    
    .chapter-tabs {
        justify-content: flex-start;
    }
    
    .quiz-type-selector {
        flex-direction: column;
        align-items: center;
    }
    
    .quiz-type-btn {
        width: 100%;
        max-width: 300px;
        justify-content: center;
    }
    
    .progress-stats {
        grid-template-columns: 1fr;
    }
    
    .stat-card {
        flex-direction: column;
        text-align: center;
    }
    
    .container {
        padding: 0 15px;
    }
}

@media (max-width: 480px) {
    .hero {
        padding: 2rem 1rem;
    }
    
    .hero h2 {
        font-size: 1.5rem;
    }
    
    .hero p {
        font-size: 1rem;
    }
    
    .chapter-card {
        padding: 1.5rem;
    }
    
    .chapter-content {
        padding: 1.5rem;
    }
    
    .question-card {
        padding: 1.5rem;
    }
    
    .stat-card {
        padding: 1.5rem;
    }
}

/* Dark mode support */
@media (prefers-color-scheme: dark) {
    :root {
        --light-color: #1e1e1e;
        --white: #2d2d2d;
        --dark-color: #ffffff;
        --gray: #b0b0b0;
        --light-gray: #404040;
    }
}

/* Print styles */
@media print {
    .header, .search-container, .footer {
        display: none;
    }
    
    .section {
        display: block !important;
        page-break-inside: avoid;
    }
    
    .chapter-card {
        break-inside: avoid;
    }
}