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

:root {
    --primary-color: #2563eb;
    --primary-hover: #1d4ed8;
    --secondary-color: #64748b;
    --success-color: #059669;
    --danger-color: #dc2626;
    --warning-color: #d97706;
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --text-muted: #94a3b8;
    --background: #ffffff;
    --background-alt: #f8fafc;
    --background-muted: #f1f5f9;
    --border-color: #e2e8f0;
    --border-light: #f1f5f9;
    --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
    --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
    --border-radius: 8px;
    --border-radius-lg: 12px;
    --font-size-xs: 0.75rem;
    --font-size-sm: 0.875rem;
    --font-size-base: 1rem;
    --font-size-lg: 1.125rem;
    --font-size-xl: 1.25rem;
    --font-size-2xl: 1.5rem;
    --font-size-3xl: 1.875rem;
    --font-size-4xl: 2.25rem;
    --line-height-tight: 1.25;
    --line-height-normal: 1.5;
    --line-height-relaxed: 1.625;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    line-height: var(--line-height-normal);
    color: var(--text-primary);
    background-color: var(--background);
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 1rem;
}

/* Header */
.header {
    background: var(--background);
    border-bottom: 1px solid var(--border-color);
    position: sticky;
    top: 0;
    z-index: 100;
}

.nav-container {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 1rem;
    max-width: 1200px;
    margin: 0 auto;
}

.logo {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    text-decoration: none;
    color: var(--text-primary);
    font-weight: 600;
    font-size: var(--font-size-lg);
}

.nav-menu {
    display: flex;
    list-style: none;
    gap: 2rem;
    align-items: center;
}

.nav-link {
    text-decoration: none;
    color: var(--text-secondary);
    font-weight: 500;
    transition: color 0.2s ease;
}

.nav-link:hover,
.nav-link.active {
    color: var(--primary-color);
}

.nav-toggle {
    display: none;
    flex-direction: column;
    background: none;
    border: none;
    cursor: pointer;
    padding: 0.5rem;
}

.nav-toggle span {
    width: 20px;
    height: 2px;
    background-color: var(--text-primary);
    margin: 2px 0;
    transition: 0.3s;
}

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 0.75rem 1.5rem;
    border-radius: var(--border-radius);
    font-weight: 500;
    text-decoration: none;
    border: none;
    cursor: pointer;
    transition: all 0.2s ease;
    font-size: var(--font-size-base);
    line-height: 1.25;
}

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

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

.btn-outline {
    background-color: transparent;
    color: var(--primary-color);
    border: 1px solid var(--primary-color);
}

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

.btn-secondary {
    background-color: var(--background-muted);
    color: var(--text-primary);
}

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

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

.btn-success:hover {
    background-color: #047857;
}

.btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

/* Hero Section */
.hero {
    padding: 4rem 0;
    background: linear-gradient(135deg, var(--background-alt) 0%, var(--background-muted) 100%);
}

.hero .container {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 3rem;
    align-items: center;
}

.hero-content h1 {
    font-size: var(--font-size-4xl);
    font-weight: 700;
    line-height: var(--line-height-tight);
    margin-bottom: 1.5rem;
    color: var(--text-primary);
}

.hero-content p {
    font-size: var(--font-size-lg);
    color: var(--text-secondary);
    margin-bottom: 2rem;
    line-height: var(--line-height-relaxed);
}

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

.hero-image img {
    width: 100%;
    height: auto;
}

/* Features */
.features {
    padding: 4rem 0;
    background: var(--background);
}

.features h2 {
    text-align: center;
    font-size: var(--font-size-3xl);
    font-weight: 700;
    margin-bottom: 3rem;
    color: var(--text-primary);
}

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

.feature-card {
    text-align: center;
    padding: 2rem;
    background: var(--background);
    border: 1px solid var(--border-light);
    border-radius: var(--border-radius-lg);
    box-shadow: var(--shadow-sm);
    transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.feature-card:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

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

.feature-card h3 {
    font-size: var(--font-size-xl);
    font-weight: 600;
    margin-bottom: 1rem;
    color: var(--text-primary);
}

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

/* Featured Courses */
.featured-courses {
    padding: 4rem 0;
    background: var(--background-alt);
}

.featured-courses h2 {
    text-align: center;
    font-size: var(--font-size-3xl);
    font-weight: 700;
    margin-bottom: 3rem;
    color: var(--text-primary);
}

.courses-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
    gap: 2rem;
    margin-bottom: 3rem;
}

.course-card {
    background: var(--background);
    border-radius: var(--border-radius-lg);
    overflow: hidden;
    box-shadow: var(--shadow-sm);
    transition: transform 0.2s ease, box-shadow 0.2s ease;
    border: 1px solid var(--border-light);
}

.course-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-lg);
}

.course-image {
    width: 100%;
    height: 200px;
    object-fit: cover;
    background: var(--background-muted);
}

.course-content {
    padding: 1.5rem;
}

.course-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    margin-bottom: 0.75rem;
}

.course-category {
    background: var(--primary-color);
    color: white;
    padding: 0.25rem 0.75rem;
    border-radius: 9999px;
    font-size: var(--font-size-xs);
    font-weight: 500;
}

.course-difficulty {
    color: var(--text-muted);
    font-size: var(--font-size-sm);
    font-weight: 500;
}

.course-title {
    font-size: var(--font-size-xl);
    font-weight: 600;
    margin-bottom: 0.75rem;
    color: var(--text-primary);
    line-height: var(--line-height-tight);
}

.course-description {
    color: var(--text-secondary);
    font-size: var(--font-size-sm);
    line-height: var(--line-height-relaxed);
    margin-bottom: 1rem;
}

.course-meta {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 1rem;
}

.course-duration {
    color: var(--text-muted);
    font-size: var(--font-size-sm);
}

.course-price {
    font-size: var(--font-size-xl);
    font-weight: 700;
    color: var(--primary-color);
}

.course-actions {
    display: flex;
    gap: 0.75rem;
}

.btn-small {
    padding: 0.5rem 1rem;
    font-size: var(--font-size-sm);
}

.section-footer {
    text-align: center;
}

/* Course Details */
.course-detail {
    padding: 2rem 0;
}

.course-detail-header {
    display: grid;
    grid-template-columns: 1fr 300px;
    gap: 3rem;
    margin-bottom: 3rem;
}

.course-detail-content h1 {
    font-size: var(--font-size-3xl);
    font-weight: 700;
    margin-bottom: 1rem;
    color: var(--text-primary);
}

.course-detail-meta {
    display: flex;
    gap: 2rem;
    margin-bottom: 1.5rem;
    flex-wrap: wrap;
}

.meta-item {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    color: var(--text-secondary);
    font-size: var(--font-size-sm);
}

.course-detail-description {
    color: var(--text-secondary);
    font-size: var(--font-size-lg);
    line-height: var(--line-height-relaxed);
}

.course-sidebar {
    background: var(--background);
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-lg);
    padding: 2rem;
    height: fit-content;
    position: sticky;
    top: 6rem;
}

.sidebar-price {
    font-size: var(--font-size-3xl);
    font-weight: 700;
    color: var(--primary-color);
    margin-bottom: 1.5rem;
}

.sidebar-actions {
    display: flex;
    flex-direction: column;
    gap: 0.75rem;
    margin-bottom: 2rem;
}

.sidebar-features {
    list-style: none;
}

.sidebar-features li {
    padding: 0.5rem 0;
    color: var(--text-secondary);
    border-bottom: 1px solid var(--border-light);
}

.sidebar-features li:last-child {
    border-bottom: none;
}

.course-sections {
    display: grid;
    gap: 3rem;
}

.course-section {
    background: var(--background);
    border: 1px solid var(--border-light);
    border-radius: var(--border-radius-lg);
    padding: 2rem;
}

.course-section h2 {
    font-size: var(--font-size-2xl);
    font-weight: 600;
    margin-bottom: 1.5rem;
    color: var(--text-primary);
}

.learning-outcomes,
.requirements-list,
.curriculum-list {
    list-style: none;
}

.learning-outcomes li,
.requirements-list li {
    padding: 0.5rem 0;
    color: var(--text-secondary);
    position: relative;
    padding-left: 1.5rem;
}

.learning-outcomes li::before {
    content: '✓';
    position: absolute;
    left: 0;
    color: var(--success-color);
    font-weight: bold;
}

.requirements-list li::before {
    content: '•';
    position: absolute;
    left: 0;
    color: var(--text-muted);
}

.curriculum-list {
    display: grid;
    gap: 0.5rem;
}

.curriculum-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem;
    background: var(--background-alt);
    border-radius: var(--border-radius);
}

.lesson-number {
    background: var(--primary-color);
    color: white;
    width: 24px;
    height: 24px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: var(--font-size-xs);
    font-weight: 600;
    margin-right: 1rem;
}

.lesson-title {
    flex: 1;
    font-weight: 500;
    color: var(--text-primary);
}

.lesson-duration {
    color: var(--text-muted);
    font-size: var(--font-size-sm);
}

.instructor-info {
    display: flex;
    gap: 1rem;
    align-items: flex-start;
}

.instructor-avatar {
    width: 60px;
    height: 60px;
    background: var(--primary-color);
    color: white;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: var(--font-size-xl);
    font-weight: 600;
}

.instructor-details h3 {
    font-size: var(--font-size-lg);
    font-weight: 600;
    margin-bottom: 0.5rem;
    color: var(--text-primary);
}

.instructor-bio {
    color: var(--text-secondary);
    line-height: var(--line-height-relaxed);
}

.faq-list {
    display: grid;
    gap: 1rem;
}

.faq-item {
    border: 1px solid var(--border-light);
    border-radius: var(--border-radius);
    overflow: hidden;
}

.faq-question {
    width: 100%;
    text-align: left;
    background: var(--background-alt);
    border: none;
    padding: 1rem;
    font-weight: 500;
    color: var(--text-primary);
    cursor: pointer;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.faq-question:hover {
    background: var(--background-muted);
}

.faq-answer {
    padding: 1rem;
    color: var(--text-secondary);
    line-height: var(--line-height-relaxed);
    display: none;
}

.faq-answer.active {
    display: block;
}

/* Courses Page */
.courses-header {
    padding: 2rem 0;
    background: var(--background-alt);
    border-bottom: 1px solid var(--border-color);
}

.courses-header h1 {
    font-size: var(--font-size-3xl);
    font-weight: 700;
    margin-bottom: 1rem;
    color: var(--text-primary);
}

.courses-controls {
    display: flex;
    gap: 1rem;
    flex-wrap: wrap;
    align-items: center;
}

.search-box {
    flex: 1;
    min-width: 280px;
    position: relative;
}

.search-input {
    width: 100%;
    padding: 0.75rem 1rem;
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius);
    font-size: var(--font-size-base);
}

.search-input:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgb(37 99 235 / 0.1);
}

.filter-select,
.sort-select {
    padding: 0.75rem 1rem;
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius);
    background: var(--background);
    font-size: var(--font-size-base);
    min-width: 150px;
}

.courses-content {
    padding: 2rem 0;
}

.courses-results {
    margin-bottom: 2rem;
    color: var(--text-secondary);
}

/* Checkout */
.checkout-header {
    padding: 2rem 0;
    background: var(--background-alt);
    border-bottom: 1px solid var(--border-color);
}

.checkout-progress {
    display: flex;
    justify-content: center;
    gap: 2rem;
    margin-bottom: 2rem;
}

.progress-step {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    color: var(--text-muted);
}

.progress-step.active {
    color: var(--primary-color);
    font-weight: 600;
}

.step-number {
    width: 32px;
    height: 32px;
    border-radius: 50%;
    background: var(--background-muted);
    color: var(--text-muted);
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 600;
}

.progress-step.active .step-number {
    background: var(--primary-color);
    color: white;
}

.checkout-content {
    padding: 2rem 0;
}

.checkout-grid {
    display: grid;
    grid-template-columns: 1fr 400px;
    gap: 3rem;
}

.checkout-form {
    background: var(--background);
    border: 1px solid var(--border-light);
    border-radius: var(--border-radius-lg);
    padding: 2rem;
}

.form-group {
    margin-bottom: 1.5rem;
}

.form-label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 500;
    color: var(--text-primary);
}

.form-input {
    width: 100%;
    padding: 0.75rem 1rem;
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius);
    font-size: var(--font-size-base);
}

.form-input:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgb(37 99 235 / 0.1);
}

.form-input.error {
    border-color: var(--danger-color);
}

.form-error {
    color: var(--danger-color);
    font-size: var(--font-size-sm);
    margin-top: 0.25rem;
}

.form-row {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 1rem;
}

.checkbox-group {
    display: flex;
    align-items: flex-start;
    gap: 0.5rem;
    margin: 1.5rem 0;
}

.checkbox-group input[type="checkbox"] {
    margin-top: 0.25rem;
}

.checkbox-group label {
    font-size: var(--font-size-sm);
    line-height: var(--line-height-relaxed);
}

.order-summary {
    background: var(--background);
    border: 1px solid var(--border-light);
    border-radius: var(--border-radius-lg);
    padding: 2rem;
    height: fit-content;
    position: sticky;
    top: 6rem;
}

.summary-item {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem 0;
    border-bottom: 1px solid var(--border-light);
}

.summary-item:last-child {
    border-bottom: none;
    font-weight: 600;
    font-size: var(--font-size-lg);
}

.payment-icons {
    display: flex;
    gap: 0.5rem;
    margin: 1rem 0;
}

.payment-icon {
    width: 40px;
    height: 24px;
    background: var(--background-muted);
    border: 1px solid var(--border-color);
    border-radius: 4px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: var(--font-size-xs);
    color: var(--text-muted);
}

/* Success Page */
.success-content {
    padding: 4rem 0;
    text-align: center;
}

.success-icon {
    width: 80px;
    height: 80px;
    background: var(--success-color);
    color: white;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 2rem;
    margin: 0 auto 2rem;
}

.success-content h1 {
    font-size: var(--font-size-3xl);
    font-weight: 700;
    margin-bottom: 1rem;
    color: var(--text-primary);
}

.success-content p {
    font-size: var(--font-size-lg);
    color: var(--text-secondary);
    margin-bottom: 2rem;
    line-height: var(--line-height-relaxed);
}

.order-details {
    background: var(--background-alt);
    border: 1px solid var(--border-light);
    border-radius: var(--border-radius-lg);
    padding: 2rem;
    margin: 2rem auto;
    max-width: 600px;
    text-align: left;
}

/* Footer */
.footer {
    background: var(--text-primary);
    color: white;
    padding: 3rem 0 1rem;
    margin-top: 4rem;
}

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

.footer-section h4 {
    font-size: var(--font-size-lg);
    font-weight: 600;
    margin-bottom: 1rem;
}

.footer-section ul {
    list-style: none;
}

.footer-section ul li {
    margin-bottom: 0.5rem;
}

.footer-section a {
    color: #cbd5e1;
    text-decoration: none;
    transition: color 0.2s ease;
}

.footer-section a:hover {
    color: white;
}

.footer-logo {
    display: flex;
    align-items: center;
    gap: 0.75rem;
    margin-bottom: 1rem;
    font-weight: 600;
    font-size: var(--font-size-lg);
}

.footer-bottom {
    border-top: 1px solid #374151;
    padding-top: 2rem;
    text-align: center;
    color: #9ca3af;
}

/* Responsive Design */
@media (max-width: 768px) {
    .nav-menu {
        display: none;
        position: absolute;
        top: 100%;
        left: 0;
        width: 100%;
        background: var(--background);
        border-top: 1px solid var(--border-color);
        flex-direction: column;
        padding: 1rem;
        gap: 1rem;
    }

    .nav-menu.active {
        display: flex;
    }

    .nav-toggle {
        display: flex;
    }

    .hero .container {
        grid-template-columns: 1fr;
        text-align: center;
    }

    .hero-content h1 {
        font-size: var(--font-size-3xl);
    }

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

    .features-grid {
        grid-template-columns: 1fr;
    }

    .courses-grid {
        grid-template-columns: 1fr;
    }

    .course-detail-header {
        grid-template-columns: 1fr;
    }

    .course-sidebar {
        position: static;
        order: -1;
    }

    .checkout-grid {
        grid-template-columns: 1fr;
    }

    .order-summary {
        position: static;
        order: -1;
    }

    .courses-controls {
        flex-direction: column;
        align-items: stretch;
    }

    .search-box {
        min-width: auto;
    }

    .form-row {
        grid-template-columns: 1fr;
    }

    .checkout-progress {
        gap: 1rem;
        font-size: var(--font-size-sm);
    }

    .progress-step span {
        display: none;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 0 0.75rem;
    }

    .hero {
        padding: 2rem 0;
    }

    .hero-content h1 {
        font-size: var(--font-size-2xl);
    }

    .features,
    .featured-courses {
        padding: 2rem 0;
    }

    .course-card,
    .feature-card,
    .checkout-form,
    .order-summary,
    .course-section {
        padding: 1rem;
    }

    .btn {
        padding: 0.625rem 1.25rem;
    }

    .hero-actions {
        flex-direction: column;
        width: 100%;
    }

    .hero-actions .btn {
        width: 100%;
    }
}

/* Print Styles */
@media print {
    .header,
    .footer,
    .nav,
    .btn,
    button {
        display: none !important;
    }

    .container {
        max-width: none;
        padding: 0;
    }

    body {
        font-size: 12pt;
        line-height: 1.4;
    }

    h1, h2, h3, h4, h5, h6 {
        page-break-after: avoid;
    }

    .course-card,
    .feature-card {
        break-inside: avoid;
        box-shadow: none;
        border: 1px solid #000;
    }
}

/* Focus Styles for Accessibility */
button:focus,
a:focus,
input:focus,
select:focus,
textarea:focus {
    outline: 2px solid var(--primary-color);
    outline-offset: 2px;
}

/* High Contrast Mode */
@media (prefers-contrast: high) {
    :root {
        --border-color: #000;
        --border-light: #666;
        --text-secondary: #000;
        --text-muted: #333;
    }
}

/* Reduced Motion */
@media (prefers-reduced-motion: reduce) {
    *,
    *::before,
    *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}