/* ========================================
   apexcolab - AI Education Platform
   Main Stylesheet
   ======================================== */

/* CSS Variables */
:root {
    --primary-color: #1a365d;
    --primary-light: #2c5282;
    --primary-dark: #0d1b2a;
    --accent-color: #3182ce;
    --accent-light: #63b3ed;
    --gradient-start: #1a365d;
    --gradient-end: #3182ce;
    --text-primary: #1a202c;
    --text-secondary: #4a5568;
    --text-muted: #718096;
    --bg-primary: #ffffff;
    --bg-secondary: #f7fafc;
    --bg-dark: #edf2f7;
    --border-color: #e2e8f0;
    --success-color: #38a169;
    --warning-color: #d69e2e;
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
    --radius-sm: 4px;
    --radius-md: 8px;
    --radius-lg: 12px;
    --radius-xl: 16px;
    --transition-fast: 0.15s ease;
    --transition-normal: 0.3s ease;
    --transition-slow: 0.5s ease;
}

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

html {
    scroll-behavior: smooth;
    font-size: 16px;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, 'Noto Sans', sans-serif;
    line-height: 1.6;
    color: var(--text-primary);
    background-color: var(--bg-primary);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

a {
    text-decoration: none;
    color: inherit;
    transition: color var(--transition-fast);
}

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

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

ul, ol {
    list-style: none;
}

/* ========================================
   Layout
   ======================================== */

.container {
    width: 100%;
    max-width: 1280px;
    margin: 0 auto;
    padding: 0 24px;
}

.section {
    padding: 80px 0;
}

.section-header {
    text-align: center;
    margin-bottom: 48px;
}

.section-title {
    font-size: 2rem;
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: 12px;
}

.section-subtitle {
    font-size: 1rem;
    color: var(--text-secondary);
}

/* ========================================
   Header & Navigation
   ======================================== */

.header {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 1000;
    background: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(10px);
    border-bottom: 1px solid var(--border-color);
    transition: box-shadow var(--transition-normal);
}

.header.scrolled {
    box-shadow: var(--shadow-md);
}

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

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

.logo img {
    height: 36px;
    width: auto;
}

.logo-text {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--primary-color);
}

.nav {
    display: flex;
    align-items: center;
    gap: 8px;
}

.nav-link {
    padding: 8px 16px;
    font-size: 0.9375rem;
    font-weight: 500;
    color: var(--text-secondary);
    border-radius: var(--radius-md);
    transition: all var(--transition-fast);
}

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

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

.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 6px;
    padding: 10px 20px;
    font-size: 0.875rem;
    font-weight: 600;
    border-radius: var(--radius-md);
    transition: all var(--transition-fast);
}

.btn-primary {
    background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
    color: white;
    box-shadow: var(--shadow-sm);
}

.btn-primary:hover {
    transform: translateY(-1px);
    box-shadow: var(--shadow-md);
}

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

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

.mobile-menu-btn {
    display: none;
    padding: 8px;
    font-size: 1.25rem;
    color: var(--text-primary);
}

/* ========================================
   Hero Section
   ======================================== */

.hero {
    position: relative;
    min-height: 100vh;
    display: flex;
    align-items: center;
    background: linear-gradient(135deg, var(--primary-dark) 0%, var(--primary-color) 50%, var(--primary-light) 100%);
    overflow: hidden;
}

.hero-bg {
    position: absolute;
    inset: 0;
    opacity: 0.3;
}

.hero-bg img {
    width: 100%;
    height: 100%;
    object-fit: cover;
}

.hero-content {
    position: relative;
    z-index: 1;
    padding-top: 64px;
    text-align: center;
    color: white;
}

.hero-badge {
    display: inline-flex;
    align-items: center;
    gap: 6px;
    padding: 6px 14px;
    background: rgba(255, 255, 255, 0.15);
    backdrop-filter: blur(10px);
    border-radius: 20px;
    font-size: 0.8125rem;
    margin-bottom: 24px;
}

.hero-title {
    font-size: 3.5rem;
    font-weight: 800;
    line-height: 1.2;
    margin-bottom: 16px;
    text-shadow: 0 2px 10px rgba(0, 0, 0, 0.2);
}

.hero-title span {
    background: linear-gradient(135deg, #63b3ed, #90cdf4);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.hero-subtitle {
    font-size: 1.125rem;
    color: rgba(255, 255, 255, 0.85);
    margin-bottom: 32px;
    max-width: 600px;
    margin-left: auto;
    margin-right: auto;
}

.hero-actions {
    display: flex;
    justify-content: center;
    gap: 16px;
    margin-bottom: 40px;
}

.hero-btn {
    padding: 14px 32px;
    font-size: 1rem;
    border-radius: var(--radius-lg);
}

.hero-btn-primary {
    background: white;
    color: var(--primary-color);
    font-weight: 600;
    box-shadow: var(--shadow-lg);
}

.hero-btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-xl);
}

.hero-btn-outline {
    border: 2px solid rgba(255, 255, 255, 0.3);
    color: white;
    background: transparent;
}

.hero-btn-outline:hover {
    background: rgba(255, 255, 255, 0.1);
    border-color: rgba(255, 255, 255, 0.5);
}

.hero-features {
    display: flex;
    justify-content: center;
    gap: 32px;
    flex-wrap: wrap;
}

.hero-feature {
    display: flex;
    align-items: center;
    gap: 8px;
    font-size: 0.875rem;
    color: rgba(255, 255, 255, 0.8);
}

.hero-feature i {
    color: #48bb78;
}

/* ========================================
   Stats Section
   ======================================== */

.stats-section {
    padding: 40px 0;
    background: white;
    border-bottom: 1px solid var(--border-color);
}

.stats-grid {
    display: grid;
    grid-template-columns: repeat(6, 1fr);
    gap: 24px;
}

.stat-item {
    text-align: center;
    padding: 16px;
}

.stat-number {
    font-size: 2rem;
    font-weight: 800;
    color: var(--primary-color);
    line-height: 1;
    margin-bottom: 4px;
}

.stat-label {
    font-size: 0.8125rem;
    color: var(--text-muted);
}

/* ========================================
   Features Section
   ======================================== */

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

.features-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 24px;
}

.feature-card {
    background: white;
    padding: 32px;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-sm);
    transition: all var(--transition-normal);
}

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

.feature-icon {
    width: 48px;
    height: 48px;
    display: flex;
    align-items: center;
    justify-content: center;
    background: linear-gradient(135deg, var(--accent-light), var(--accent-color));
    border-radius: var(--radius-md);
    margin-bottom: 16px;
    font-size: 1.25rem;
    color: white;
}

.feature-title {
    font-size: 1.125rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 8px;
}

.feature-desc {
    font-size: 0.875rem;
    color: var(--text-secondary);
    line-height: 1.6;
}

/* ========================================
   Courses Section
   ======================================== */

.courses-section {
    background: white;
}

.courses-grid {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 24px;
}

.course-card {
    background: white;
    border-radius: var(--radius-lg);
    overflow: hidden;
    box-shadow: var(--shadow-sm);
    border: 1px solid var(--border-color);
    transition: all var(--transition-normal);
}

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

.course-image {
    position: relative;
    aspect-ratio: 16/9;
    overflow: hidden;
}

.course-image img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    transition: transform var(--transition-slow);
}

.course-card:hover .course-image img {
    transform: scale(1.05);
}

.course-badge {
    position: absolute;
    top: 12px;
    left: 12px;
    padding: 4px 10px;
    background: rgba(26, 54, 93, 0.9);
    color: white;
    font-size: 0.6875rem;
    font-weight: 600;
    border-radius: 4px;
    text-transform: uppercase;
}

.course-content {
    padding: 20px;
}

.course-title {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-primary);
    margin-bottom: 8px;
    line-height: 1.4;
}

.course-desc {
    font-size: 0.8125rem;
    color: var(--text-muted);
    margin-bottom: 16px;
    line-height: 1.5;
}

.course-meta {
    display: flex;
    align-items: center;
    gap: 16px;
    margin-bottom: 16px;
}

.course-meta-item {
    display: flex;
    align-items: center;
    gap: 4px;
    font-size: 0.75rem;
    color: var(--text-muted);
}

.course-btn {
    width: 100%;
    padding: 10px;
    background: linear-gradient(135deg, var(--gradient-start), var(--gradient-end));
    color: white;
    font-size: 0.875rem;
    font-weight: 600;
    border-radius: var(--radius-md);
    transition: all var(--transition-fast);
}

.course-btn:hover {
    opacity: 0.9;
    transform: translateY(-1px);
}

/* ========================================
   Footer
   ======================================== */

.footer {
    background: var(--primary-dark);
    color: white;
    padding: 60px 0 24px;
}

.footer-grid {
    display: grid;
    grid-template-columns: 2fr 1fr 1fr 1fr;
    gap: 48px;
    margin-bottom: 48px;
}

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

.footer-logo {
    display: flex;
    align-items: center;
    gap: 10px;
    margin-bottom: 16px;
}

.footer-logo img {
    height: 32px;
}

.footer-logo-text {
    font-size: 1.125rem;
    font-weight: 700;
}

.footer-desc {
    font-size: 0.875rem;
    color: rgba(255, 255, 255, 0.7);
    line-height: 1.6;
}

.footer-title {
    font-size: 0.875rem;
    font-weight: 600;
    margin-bottom: 16px;
    color: white;
}

.footer-links {
    display: flex;
    flex-direction: column;
    gap: 10px;
}

.footer-link {
    font-size: 0.875rem;
    color: rgba(255, 255, 255, 0.7);
    transition: color var(--transition-fast);
}

.footer-link:hover {
    color: white;
}

.footer-bottom {
    padding-top: 24px;
    border-top: 1px solid rgba(255, 255, 255, 0.1);
    text-align: center;
    font-size: 0.8125rem;
    color: rgba(255, 255, 255, 0.5);
}

/* ========================================
   Responsive Design
   ======================================== */

@media (max-width: 1024px) {
    .stats-grid {
        grid-template-columns: repeat(3, 1fr);
    }
    
    .features-grid,
    .courses-grid {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .footer-grid {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 768px) {
    .nav {
        display: none;
        position: absolute;
        top: 64px;
        left: 0;
        right: 0;
        background: white;
        flex-direction: column;
        padding: 16px;
        border-bottom: 1px solid var(--border-color);
        box-shadow: var(--shadow-lg);
    }
    
    .nav.active {
        display: flex;
    }
    
    .nav-link {
        width: 100%;
        padding: 12px 16px;
    }
    
    .mobile-menu-btn {
        display: block;
    }
    
    .header-actions .btn-outline {
        display: none;
    }
    
    .hero-title {
        font-size: 2.25rem;
    }
    
    .hero-subtitle {
        font-size: 1rem;
    }
    
    .hero-actions {
        flex-direction: column;
        align-items: center;
    }
    
    .stats-grid {
        grid-template-columns: repeat(2, 1fr);
    }
    
    .features-grid,
    .courses-grid {
        grid-template-columns: 1fr;
    }
    
    .footer-grid {
        grid-template-columns: 1fr;
        gap: 32px;
    }
    
    .section {
        padding: 60px 0;
    }
    
    .section-title {
        font-size: 1.5rem;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 0 16px;
    }
    
    .hero-title {
        font-size: 1.875rem;
    }
    
    .stats-grid {
        grid-template-columns: 1fr;
    }
}