/* CSS Variables */
:root {
    --primary: #4F46E5;
    --primary-hover: #4338CA;
    --secondary: #10B981;
    --accent: #F59E0B;
    --dark: #1F2937;
    --gray-900: #111827;
    --gray-800: #1F2937;
    --gray-700: #374151;
    --gray-600: #4B5563;
    --gray-500: #6B7280;
    --gray-400: #9CA3AF;
    --gray-300: #D1D5DB;
    --gray-200: #E5E7EB;
    --gray-100: #F3F4F6;
    --gray-50: #F9FAFB;
    --white: #FFFFFF;
    --error: #EF4444;
    --success: #10B981;
    --radius-sm: 4px;
    --radius-md: 8px;
    --radius-lg: 12px;
    --radius-xl: 16px;
    --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1);
}

/* Reset */
*, *::before, *::after {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

html {
    scroll-behavior: smooth;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    line-height: 1.6;
    color: var(--gray-800);
    background: var(--gray-50);
}

a {
    text-decoration: none;
    color: inherit;
}

img {
    max-width: 100%;
    height: auto;
}

button {
    cursor: pointer;
    border: none;
    background: none;
    font: inherit;
}

input, textarea {
    font: inherit;
}

ul, ol {
    list-style: none;
}

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

/* Header */
.header {
    position: sticky;
    top: 0;
    z-index: 100;
    background: var(--white);
    border-bottom: 1px solid var(--gray-200);
    backdrop-filter: blur(10px);
}

.header .container {
    display: flex;
    align-items: center;
    justify-content: space-between;
    height: 64px;
}

.logo {
    display: flex;
    align-items: center;
    gap: 8px;
    font-size: 24px;
    font-weight: 700;
    color: var(--primary);
}

.logo-icon {
    font-size: 28px;
}

.nav {
    display: flex;
    gap: 32px;
}

.nav-link {
    font-weight: 500;
    color: var(--gray-600);
    transition: color 0.2s;
}

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

.header-actions {
    display: flex;
    align-items: center;
    gap: 12px;
}

.user-menu {
    display: flex;
    align-items: center;
    gap: 12px;
}

.user-name {
    font-weight: 500;
    color: var(--gray-700);
}

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 10px 20px;
    font-weight: 500;
    border-radius: var(--radius-md);
    transition: all 0.2s;
}

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

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

.btn-outline {
    border: 2px solid var(--primary);
    color: var(--primary);
}

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

.btn-ghost {
    color: var(--gray-600);
}

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

.btn-lg {
    padding: 14px 28px;
    font-size: 18px;
}

.btn-block {
    width: 100%;
}

/* Hero Section */
.hero {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: var(--white);
    padding: 80px 0;
    text-align: center;
}

.hero-content {
    max-width: 700px;
    margin: 0 auto 48px;
}

.hero-title {
    font-size: 56px;
    font-weight: 800;
    margin-bottom: 20px;
    line-height: 1.2;
}

.hero-subtitle {
    font-size: 20px;
    opacity: 0.9;
    margin-bottom: 32px;
}

.hero-actions {
    display: flex;
    gap: 16px;
    justify-content: center;
}

.hero-stats {
    display: flex;
    justify-content: center;
    gap: 64px;
}

.stat-item {
    text-align: center;
}

.stat-number {
    display: block;
    font-size: 40px;
    font-weight: 700;
}

.stat-label {
    font-size: 16px;
    opacity: 0.8;
}

/* Sections */
.section {
    padding: 64px 0;
}

.section-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 32px;
}

.section-title {
    font-size: 32px;
    font-weight: 700;
    color: var(--gray-900);
}

.section-link {
    color: var(--primary);
    font-weight: 500;
}

/* Categories Grid */
.categories-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
    gap: 20px;
}

.category-card {
    background: var(--white);
    padding: 32px 20px;
    border-radius: var(--radius-lg);
    text-align: center;
    transition: all 0.3s;
    border: 1px solid var(--gray-200);
}

.category-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-lg);
    border-color: var(--primary);
}

.category-icon {
    font-size: 48px;
    margin-bottom: 12px;
}

.category-name {
    font-size: 18px;
    font-weight: 600;
    color: var(--gray-800);
}

.category-desc {
    font-size: 14px;
    color: var(--gray-500);
    margin-top: 8px;
}

/* Courses Grid */
.courses-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 24px;
}

.course-card {
    background: var(--white);
    border-radius: var(--radius-lg);
    overflow: hidden;
    transition: all 0.3s;
    border: 1px solid var(--gray-200);
}

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

.course-cover {
    height: 160px;
    background: linear-gradient(135deg, var(--primary), var(--secondary));
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 64px;
}

.course-info {
    padding: 20px;
}

.course-category {
    font-size: 12px;
    color: var(--primary);
    font-weight: 600;
    text-transform: uppercase;
}

.course-title {
    font-size: 18px;
    font-weight: 600;
    margin: 8px 0;
    color: var(--gray-800);
}

.course-meta {
    display: flex;
    align-items: center;
    gap: 16px;
    font-size: 14px;
    color: var(--gray-500);
}

.course-price {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-top: 16px;
    padding-top: 16px;
    border-top: 1px solid var(--gray-100);
}

.price-current {
    font-size: 24px;
    font-weight: 700;
    color: var(--error);
}

.price-original {
    font-size: 16px;
    color: var(--gray-400);
    text-decoration: line-through;
}

/* Blog Grid */
.blog-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
    gap: 24px;
}

.blog-card {
    background: var(--white);
    border-radius: var(--radius-lg);
    overflow: hidden;
    transition: all 0.3s;
    border: 1px solid var(--gray-200);
}

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

.blog-content {
    padding: 24px;
}

.blog-category {
    display: inline-block;
    padding: 4px 12px;
    background: var(--gray-100);
    border-radius: 20px;
    font-size: 12px;
    color: var(--gray-600);
    font-weight: 500;
}

.blog-title {
    font-size: 18px;
    font-weight: 600;
    margin: 12px 0;
    color: var(--gray-800);
    line-height: 1.4;
}

.blog-excerpt {
    font-size: 14px;
    color: var(--gray-500);
    line-height: 1.6;
}

.blog-meta {
    display: flex;
    align-items: center;
    gap: 16px;
    margin-top: 16px;
    font-size: 13px;
    color: var(--gray-400);
}

/* CTA Section */
.cta-section {
    background: var(--gray-900);
    color: var(--white);
    text-align: center;
}

.cta-title {
    font-size: 36px;
    font-weight: 700;
    margin-bottom: 16px;
}

.cta-subtitle {
    font-size: 18px;
    opacity: 0.8;
    margin-bottom: 32px;
}

/* Footer */
.footer {
    background: var(--gray-800);
    color: var(--gray-300);
    padding: 48px 0 24px;
}

.footer-content {
    display: flex;
    justify-content: space-between;
    margin-bottom: 32px;
}

.footer-brand {
    max-width: 300px;
}

.footer-brand .logo-text {
    color: var(--white);
}

.footer-desc {
    margin-top: 12px;
    font-size: 14px;
    opacity: 0.7;
}

.footer-links {
    display: flex;
    gap: 64px;
}

.footer-column h4 {
    color: var(--white);
    font-weight: 600;
    margin-bottom: 16px;
}

.footer-column a {
    display: block;
    font-size: 14px;
    margin-bottom: 8px;
    opacity: 0.7;
    transition: opacity 0.2s;
}

.footer-column a:hover {
    opacity: 1;
}

.footer-bottom {
    padding-top: 24px;
    border-top: 1px solid var(--gray-700);
    text-align: center;
    font-size: 14px;
    opacity: 0.6;
}

/* Modal */
.modal {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    z-index: 1000;
    display: flex;
    align-items: center;
    justify-content: center;
}

.modal-backdrop {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(0, 0, 0, 0.5);
}

.modal-content {
    position: relative;
    background: var(--white);
    border-radius: var(--radius-lg);
    padding: 32px;
    width: 100%;
    max-width: 400px;
    box-shadow: var(--shadow-xl);
}

.modal-close {
    position: absolute;
    top: 16px;
    right: 16px;
    font-size: 24px;
    color: var(--gray-400);
}

.modal-close:hover {
    color: var(--gray-600);
}

/* Auth */
.auth-tabs {
    display: flex;
    margin-bottom: 24px;
    border-bottom: 1px solid var(--gray-200);
}

.auth-tab {
    flex: 1;
    padding: 12px;
    font-weight: 500;
    color: var(--gray-500);
    border-bottom: 2px solid transparent;
    transition: all 0.2s;
}

.auth-tab.active {
    color: var(--primary);
    border-bottom-color: var(--primary);
}

.auth-form {
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.form-group {
    display: flex;
    flex-direction: column;
    gap: 6px;
}

.form-group label {
    font-weight: 500;
    font-size: 14px;
    color: var(--gray-700);
}

.form-group input {
    padding: 12px;
    border: 1px solid var(--gray-300);
    border-radius: var(--radius-md);
    transition: border-color 0.2s;
}

.form-group input:focus {
    outline: none;
    border-color: var(--primary);
}

/* Utility */
.hidden {
    display: none !important;
}

/* Page Header (for inner pages) */
.page-header {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: var(--white);
    padding: 48px 0;
    text-align: center;
}

.page-title {
    font-size: 40px;
    font-weight: 700;
    margin-bottom: 12px;
}

.page-subtitle {
    font-size: 18px;
    opacity: 0.9;
}

/* Filter Bar */
.filter-bar {
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 32px;
    flex-wrap: wrap;
}

.filter-btn {
    padding: 8px 16px;
    border-radius: 20px;
    font-size: 14px;
    font-weight: 500;
    background: var(--white);
    border: 1px solid var(--gray-200);
    color: var(--gray-600);
    transition: all 0.2s;
}

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

/* Empty State */
.empty-state {
    text-align: center;
    padding: 64px 20px;
    color: var(--gray-500);
}

.empty-state-icon {
    font-size: 64px;
    margin-bottom: 16px;
}

/* Responsive */
@media (max-width: 768px) {
    .hero-title {
        font-size: 36px;
    }

    .hero-subtitle {
        font-size: 18px;
    }

    .hero-stats {
        gap: 32px;
    }

    .stat-number {
        font-size: 28px;
    }

    .nav {
        display: none;
    }

    .section-title {
        font-size: 24px;
    }

    .footer-content {
        flex-direction: column;
        gap: 32px;
    }

    .footer-links {
        gap: 32px;
    }
}