:root {
    --primary-color: #4f46e5;
    --primary-hover: #4338ca;
    --secondary-color: #1e1b4b;
    --bg-color: #0f172a;
    --bg-secondary: #1e293b;
    --bg-glass: rgba(30, 41, 59, 0.7);
    --text-primary: #f8fafc;
    --text-secondary: #94a3b8;
    --border-color: rgba(255, 255, 255, 0.1);
    --success-color: #22c55e;
    --error-color: #ef4444;
    --accent-color: #818cf8;
}

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

body {
    font-family: 'Inter', sans-serif;
    background-color: var(--bg-color);
    color: var(--text-primary);
    line-height: 1.6;
    overflow-x: hidden;
}

a {
    text-decoration: none;
    color: inherit;
    transition: all 0.3s ease;
}

ul {
    list-style: none;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 1.5rem;
}

/* Navbar */
.navbar {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    z-index: 1000;
    background: var(--bg-glass);
    backdrop-filter: blur(12px);
    border-bottom: 1px solid var(--border-color);
    padding: 1rem 0;
}

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

.navbar-brand {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    font-weight: 700;
    font-size: 1.25rem;
}

.logo-icon {
    width: 40px;
    height: 40px;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    border-radius: 8px;
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
    font-size: 1.2rem;
    font-weight: 700;
}

.navbar-links {
    display: flex;
    align-items: center;
    gap: 2rem;
}

.navbar-links a:not(.btn) {
    color: var(--text-secondary);
}

.navbar-links a:not(.btn):hover {
    color: var(--text-primary);
}

/* Buttons */
.btn {
    display: inline-block;
    padding: 0.75rem 1.5rem;
    border-radius: 8px;
    font-weight: 600;
    text-align: center;
    cursor: pointer;
    border: none;
    transition: all 0.3s ease;
    font-size: 1rem;
}

.btn-sm {
    padding: 0.5rem 1rem;
    font-size: 0.875rem;
}

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

.btn-primary:hover {
    background-color: var(--primary-hover);
    transform: translateY(-2px);
}

.btn-secondary {
    background-color: var(--bg-secondary);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
}

.btn-secondary:hover {
    border-color: var(--primary-color);
    transform: translateY(-2px);
}

/* Hero Section */
.hero {
    padding-top: 8rem;
    padding-bottom: 4rem;
    min-height: 80vh;
    display: flex;
    align-items: center;
}

.hero-container {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 4rem;
    align-items: center;
}

.hero-title {
    font-size: 3.5rem;
    line-height: 1.1;
    font-weight: 800;
    margin-bottom: 1.5rem;
}

.text-highlight {
    background: linear-gradient(to right, #818cf8, #6366f1);
    background-clip: text;
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
}

.hero-subtitle {
    font-size: 1.25rem;
    color: var(--text-secondary);
    margin-bottom: 2.5rem;
    max-width: 500px;
}

.hero-buttons {
    display: flex;
    gap: 1rem;
    flex-wrap: wrap;
}

.justify-center {
    justify-content: center;
}

.store-badge {
    background-color: var(--bg-secondary);
    border: 1px solid var(--border-color);
    padding: 0.5rem 1.25rem;
    border-radius: 8px;
    display: flex;
    flex-direction: column;
    align-items: flex-start;
    min-width: 160px;
    transition: all 0.3s ease;
}

.store-badge span {
    font-size: 0.75rem;
    color: var(--text-secondary);
}

.store-badge strong {
    font-size: 1.125rem;
    font-weight: 600;
}

.store-badge:hover {
    border-color: var(--primary-color);
    background-color: rgba(79, 70, 229, 0.1);
}

.app-mockup {
    background: #222;
    border-radius: 20px;
    padding: 10px;
    border: 1px solid #333;
    box-shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.5);
    max-width: 320px;
    margin: 0 auto;
    position: relative;
    aspect-ratio: 9/19;
}

.mockup-screen {
    background: var(--bg-color);
    border-radius: 12px;
    height: 100%;
    overflow: hidden;
    position: relative;
}

.mockup-header {
    background: var(--bg-secondary);
    padding: 1rem;
    border-bottom: 1px solid var(--border-color);
    font-weight: 600;
    text-align: center;
}

.mockup-body {
    padding: 1rem;
}

.mockup-item {
    background: var(--bg-secondary);
    height: 60px;
    margin-bottom: 1rem;
    border-radius: 8px;
    animation: pulse 2s infinite;
}

.mockup-item.short {
    width: 60%;
}

@keyframes pulse {
    0% {
        opacity: 0.6;
    }

    50% {
        opacity: 1;
    }

    100% {
        opacity: 0.6;
    }
}

/* Sections */
.section {
    padding: 4rem 0;
}

.section-title {
    text-align: center;
    font-size: 2.25rem;
    font-weight: 700;
    margin-bottom: 3rem;
}

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

/* Text Utilities */
.text-center {
    text-align: center;
}

.text-success {
    color: var(--success-color);
    font-weight: 600;
}

.text-error {
    color: var(--error-color);
    font-weight: 600;
}

.mt-4 {
    margin-top: 2rem;
}

/* Features Grid */
.features-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 2rem;
}

.feature-card {
    background: var(--bg-glass);
    border: 1px solid var(--border-color);
    padding: 2rem;
    border-radius: 12px;
    text-align: center;
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
    overflow: hidden;
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
}

.feature-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 100%;
    background: radial-gradient(800px circle at var(--mouse-x, 50%) var(--mouse-y, -10%), rgba(255, 255, 255, 0.06), transparent 40%);
    opacity: 0;
    transition: opacity 0.4s ease;
    pointer-events: none;
    z-index: 1;
}

.feature-card:hover {
    transform: translateY(-8px) scale(1.02);
    border-color: var(--primary-color);
    box-shadow: 0 20px 40px -10px rgba(0, 0, 0, 0.5);
}

.feature-card:hover::before {
    opacity: 1;
}

.feature-icon {
    font-size: 2.5rem;
    margin-bottom: 1rem;
    display: inline-block;
}

.feature-card h3 {
    margin-bottom: 0.5rem;
    font-size: 1.25rem;
}

.feature-card p {
    color: var(--text-secondary);
}

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

.chapter-card {
    background: var(--bg-glass);
    border: 1px solid var(--border-color);
    padding: 1.5rem;
    border-radius: 12px;
    display: flex;
    align-items: center;
    gap: 1rem;
    transition: all 0.4s cubic-bezier(0.4, 0, 0.2, 1);
    position: relative;
    overflow: hidden;
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
}

.chapter-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 100%;
    background: radial-gradient(800px circle at var(--mouse-x, 50%) var(--mouse-y, -10%), rgba(255, 255, 255, 0.06), transparent 40%);
    opacity: 0;
    transition: opacity 0.4s ease;
    pointer-events: none;
    z-index: 1;
}

.chapter-card:hover:not(.disabled) {
    background: var(--bg-secondary);
    border-color: var(--primary-color);
    transform: translateX(8px) scale(1.02);
    box-shadow: 0 15px 30px -10px rgba(0, 0, 0, 0.4);
}

.chapter-card:hover:not(.disabled)::before {
    opacity: 1;
}

.chapter-card.disabled {
    opacity: 0.6;
    cursor: default;
    pointer-events: none;
}

.chapter-number {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--text-secondary);
    opacity: 0.5;
    min-width: 2.5rem;
}

.chapter-name {
    font-weight: 500;
    font-size: 1.1rem;
}

/* ============================================
   CHAPTER PAGE STYLES
   ============================================ */

/* Breadcrumb */
.breadcrumb {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-size: 0.875rem;
    color: var(--text-secondary);
    margin-bottom: 2rem;
    padding-top: 6rem;
    flex-wrap: wrap;
}

.breadcrumb a {
    color: var(--accent-color);
}

.breadcrumb a:hover {
    color: var(--text-primary);
    text-decoration: underline;
}

.breadcrumb span {
    color: var(--text-secondary);
}

/* Chapter Title */
.chapter-title {
    font-size: 2.25rem;
    font-weight: 800;
    margin-bottom: 2.5rem;
    line-height: 1.2;
    background: linear-gradient(135deg, var(--text-primary), var(--accent-color));
    background-clip: text;
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
}

/* Notes Content */
.notes-content {
    background: var(--bg-glass);
    border: 1px solid var(--border-color);
    border-radius: 16px;
    padding: 2.5rem;
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    margin-bottom: 2rem;
}

.notes-content section {
    margin-bottom: 2.5rem;
    padding-bottom: 2rem;
    border-bottom: 1px solid var(--border-color);
}

.notes-content section:last-child {
    border-bottom: none;
    margin-bottom: 0;
    padding-bottom: 0;
}

.notes-content h2 {
    font-size: 1.4rem;
    font-weight: 700;
    color: var(--accent-color);
    margin-bottom: 1rem;
    padding-left: 0.75rem;
    border-left: 3px solid var(--primary-color);
}

.notes-content h3 {
    font-size: 1.15rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 0.75rem;
    margin-top: 1.25rem;
}

.notes-content p {
    color: var(--text-secondary);
    margin-bottom: 0.75rem;
    line-height: 1.8;
}

.notes-content ul {
    list-style: disc;
    padding-left: 1.5rem;
    color: var(--text-secondary);
}

.notes-content ul li {
    margin-bottom: 0.6rem;
    line-height: 1.75;
}

.notes-content ul li strong {
    color: var(--text-primary);
}

.notes-content ol {
    list-style: decimal;
    padding-left: 1.5rem;
    color: var(--text-secondary);
}

.notes-content ol li {
    margin-bottom: 0.6rem;
    line-height: 1.75;
}

/* Highlight Box */
.highlight-box {
    background: rgba(79, 70, 229, 0.15);
    border: 1px solid rgba(79, 70, 229, 0.4);
    border-left: 4px solid var(--primary-color);
    border-radius: 8px;
    padding: 1rem 1.25rem;
    margin: 1rem 0;
    color: var(--text-primary);
    font-size: 0.95rem;
    line-height: 1.7;
}

.highlight-box strong {
    color: var(--accent-color);
}

/* Formula Box */
.formula-box {
    background: rgba(34, 197, 94, 0.1);
    border: 1px solid rgba(34, 197, 94, 0.3);
    border-radius: 8px;
    padding: 1rem 1.25rem;
    margin: 1rem 0;
    font-family: 'Courier New', monospace;
    font-size: 0.95rem;
    color: #86efac;
    text-align: center;
}

/* Comparison Table */
.comparison-table {
    width: 100%;
    border-collapse: collapse;
    margin: 1rem 0;
    font-size: 0.9rem;
    border-radius: 8px;
    overflow: hidden;
}

.comparison-table th {
    background: var(--primary-color);
    color: white;
    padding: 0.75rem 1rem;
    text-align: left;
    font-weight: 600;
}

.comparison-table td {
    padding: 0.75rem 1rem;
    border-bottom: 1px solid var(--border-color);
    color: var(--text-secondary);
    vertical-align: top;
}

.comparison-table tr:nth-child(even) td {
    background: rgba(30, 41, 59, 0.5);
}

.comparison-table tr:last-child td {
    border-bottom: none;
}

.comparison-table td strong {
    color: var(--text-primary);
}

/* ============================================
   QUIZ STYLES
   ============================================ */

.quiz-container {
    background: var(--bg-glass);
    border: 1px solid var(--border-color);
    border-radius: 16px;
    overflow: hidden;
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    margin-bottom: 3rem;
}

.quiz-header {
    background: var(--bg-secondary);
    padding: 1.25rem 2rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    border-bottom: 1px solid var(--border-color);
}

.quiz-header h3 {
    font-size: 1.2rem;
    font-weight: 700;
    color: var(--accent-color);
}

#question-progress {
    font-size: 0.875rem;
    color: var(--text-secondary);
    background: rgba(79, 70, 229, 0.2);
    padding: 0.3rem 0.75rem;
    border-radius: 20px;
    border: 1px solid rgba(79, 70, 229, 0.3);
}

.quiz-body {
    padding: 2rem;
}

.question-text {
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 1.5rem;
    line-height: 1.7;
}

.options-list {
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
}

.quiz-option {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: 10px;
    padding: 1rem 1.25rem;
    display: flex;
    align-items: center;
    gap: 1rem;
    cursor: pointer;
    transition: all 0.25s ease;
}

.quiz-option:hover:not(.correct):not(.wrong):not(.disabled) {
    border-color: var(--primary-color);
    background: rgba(79, 70, 229, 0.15);
    transform: translateX(4px);
}

.quiz-option.selected {
    border-color: var(--primary-color);
    background: rgba(79, 70, 229, 0.2);
}

.quiz-option.correct {
    border-color: var(--success-color);
    background: rgba(34, 197, 94, 0.15);
    cursor: default;
}

.quiz-option.wrong {
    border-color: var(--error-color);
    background: rgba(239, 68, 68, 0.15);
    cursor: default;
}

.quiz-option.disabled {
    opacity: 0.5;
    cursor: default;
}

.option-letter {
    width: 32px;
    height: 32px;
    min-width: 32px;
    background: rgba(79, 70, 229, 0.2);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 700;
    font-size: 0.85rem;
    color: var(--accent-color);
}

.quiz-option.correct .option-letter {
    background: rgba(34, 197, 94, 0.3);
    color: var(--success-color);
}

.quiz-option.wrong .option-letter {
    background: rgba(239, 68, 68, 0.3);
    color: var(--error-color);
}

.option-text {
    color: var(--text-primary);
    font-size: 0.95rem;
    line-height: 1.5;
}

.feedback {
    margin-top: 1.25rem;
    padding: 0.875rem 1.25rem;
    border-radius: 8px;
    font-size: 0.95rem;
    line-height: 1.6;
    color: var(--text-secondary);
    background: var(--bg-secondary);
    border-left: 3px solid var(--primary-color);
    min-height: 0;
}

.feedback:empty {
    display: none;
}

.quiz-footer {
    padding: 1.25rem 2rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    border-top: 1px solid var(--border-color);
    background: var(--bg-secondary);
}

/* Quiz Results */
.quiz-results {
    padding: 3rem 2rem;
}

.quiz-results h3 {
    font-size: 1.75rem;
    font-weight: 800;
    margin-bottom: 1.5rem;
    color: var(--accent-color);
}

.score-card {
    margin: 1.5rem auto;
    display: inline-block;
}

.score-circle {
    width: 120px;
    height: 120px;
    border-radius: 50%;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    display: flex;
    align-items: center;
    justify-content: center;
    margin: 0 auto 1rem;
    box-shadow: 0 0 30px rgba(79, 70, 229, 0.4);
}

.score-circle span {
    font-size: 1.5rem;
    font-weight: 800;
    color: white;
}

.score-card p {
    color: var(--text-secondary);
    font-size: 1.1rem;
    margin-bottom: 1.5rem;
}

.quiz-results .btn {
    margin: 0.5rem;
}

/* Footer */
.footer {
    border-top: 1px solid var(--border-color);
    padding-top: 4rem;
    padding-bottom: 2rem;
    margin-top: auto;
}

.footer-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 2rem;
    margin-bottom: 2rem;
}

.footer-logo {
    font-weight: 700;
    font-size: 1.25rem;
}

.footer-content p {
    color: var(--text-secondary);
    max-width: 500px;
    font-size: 0.9rem;
}

.footer-links {
    display: flex;
    gap: 1.5rem;
}

.footer-links a {
    color: var(--text-secondary);
    font-size: 0.9rem;
    transition: color 0.2s ease;
}

.footer-links a:hover {
    color: var(--accent-color);
}

.footer-bottom {
    text-align: center;
    color: var(--text-secondary);
    font-size: 0.875rem;
    padding-top: 2rem;
    border-top: 1px solid var(--border-color);
}

/* Mobile Responsive */
@media (max-width: 768px) {
    .hero-container {
        grid-template-columns: 1fr;
        text-align: center;
    }

    .hero-buttons {
        justify-content: center;
    }

    .hero-description {
        margin: 0 auto 2rem;
    }

    .navbar-links {
        display: none;
    }

    .hero-title {
        font-size: 2.5rem;
    }

    .chapter-title {
        font-size: 1.75rem;
    }

    .notes-content {
        padding: 1.5rem;
    }

    .quiz-header,
    .quiz-body,
    .quiz-footer {
        padding: 1rem 1.25rem;
    }

    .comparison-table {
        font-size: 0.8rem;
    }

    .comparison-table th,
    .comparison-table td {
        padding: 0.5rem 0.75rem;
    }
}