/* ==========================================
   PYTHON CHO BÉ TÈO - STYLESHEET
   Màu sắc vui nhộn, thân thiện cho trẻ em
   ========================================== */

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

:root {
    /* Màu chủ đạo */
    --primary-color: #FF6B6B;
    --secondary-color: #4ECDC4;
    --accent-color: #FFE66D;
    --success-color: #51CF66;
    --purple-color: #9B59B6;
    --orange-color: #FF8C42;
    
    /* Màu nền */
    --bg-light: #F7F9FC;
    --bg-white: #FFFFFF;
    --bg-card: #FFFFFF;
    
    /* Màu chữ */
    --text-dark: #2C3E50;
    --text-gray: #718096;
    --text-light: #A0AEC0;
    
    /* Shadows */
    --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.08);
    --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 8px 24px rgba(0, 0, 0, 0.12);
    --shadow-hover: 0 12px 32px rgba(0, 0, 0, 0.15);
    
    /* Spacing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 1rem;
    --spacing-md: 1.5rem;
    --spacing-lg: 2rem;
    --spacing-xl: 3rem;
    
    /* Border Radius */
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 16px;
    --radius-full: 9999px;
    
    /* Transitions */
    --transition: all 0.3s ease;
}

body {
    font-family: 'Quicksand', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: var(--text-dark);
    line-height: 1.6;
    min-height: 100vh;
    padding-top: 80px;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing-md);
}

/* ==========================================
   HEADER & NAVIGATION
   ========================================== */

.header {
    background: var(--bg-white);
    box-shadow: var(--shadow-md);
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 1000;
    padding: var(--spacing-sm) 0;
}

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

.logo {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--primary-color);
}

.logo i {
    font-size: 2rem;
    animation: bounce 2s infinite;
}

@keyframes bounce {
    0%, 100% { transform: translateY(0); }
    50% { transform: translateY(-5px); }
}

.nav-menu {
    display: flex;
    list-style: none;
    gap: var(--spacing-md);
}

.nav-link {
    display: flex;
    align-items: center;
    gap: var(--spacing-xs);
    padding: var(--spacing-xs) var(--spacing-md);
    border-radius: var(--radius-full);
    text-decoration: none;
    color: var(--text-dark);
    font-weight: 600;
    transition: var(--transition);
}

.nav-link:hover,
.nav-link.active {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    transform: translateY(-2px);
}

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

/* ==========================================
   HERO SECTION
   ========================================== */

.hero {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    padding: var(--spacing-xl) 0;
    color: white;
    text-align: center;
}

.hero-content {
    max-width: 800px;
    margin: 0 auto;
}

.hero-title {
    font-size: 3rem;
    font-weight: 700;
    margin-bottom: var(--spacing-sm);
    animation: fadeInDown 0.8s ease;
}

.hero-subtitle {
    font-size: 1.5rem;
    margin-bottom: var(--spacing-sm);
    opacity: 0.95;
    animation: fadeInDown 1s ease;
}

.hero-description {
    font-size: 1.1rem;
    margin-bottom: var(--spacing-lg);
    opacity: 0.9;
    animation: fadeInDown 1.2s ease;
}

@keyframes fadeInDown {
    from {
        opacity: 0;
        transform: translateY(-20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.hero-stats {
    display: flex;
    justify-content: center;
    gap: var(--spacing-lg);
    margin-bottom: var(--spacing-lg);
    flex-wrap: wrap;
}

.stat-box {
    background: rgba(255, 255, 255, 0.2);
    backdrop-filter: blur(10px);
    padding: var(--spacing-md);
    border-radius: var(--radius-lg);
    min-width: 150px;
    transition: var(--transition);
}

.stat-box:hover {
    background: rgba(255, 255, 255, 0.3);
    transform: translateY(-5px);
}

.stat-box i {
    font-size: 2rem;
    margin-bottom: var(--spacing-xs);
}

.stat-number {
    font-size: 2.5rem;
    font-weight: 700;
    margin-bottom: var(--spacing-xs);
}

.stat-label {
    font-size: 0.9rem;
    opacity: 0.9;
}

.btn-primary {
    display: inline-flex;
    align-items: center;
    gap: var(--spacing-xs);
    padding: var(--spacing-md) var(--spacing-xl);
    background: white;
    color: var(--primary-color);
    text-decoration: none;
    border-radius: var(--radius-full);
    font-weight: 700;
    font-size: 1.1rem;
    box-shadow: var(--shadow-lg);
    transition: var(--transition);
}

.btn-primary:hover {
    transform: translateY(-3px);
    box-shadow: var(--shadow-hover);
}

/* ==========================================
   PROGRESS SECTION
   ========================================== */

.progress-section {
    background: var(--bg-white);
    padding: var(--spacing-xl) 0;
}

.section-title {
    text-align: center;
    font-size: 2.5rem;
    font-weight: 700;
    color: var(--text-dark);
    margin-bottom: var(--spacing-lg);
}

.progress-bar-container {
    max-width: 600px;
    margin: 0 auto var(--spacing-lg);
    background: #E2E8F0;
    height: 40px;
    border-radius: var(--radius-full);
    overflow: hidden;
    box-shadow: var(--shadow-sm);
    position: relative;
}

.progress-bar {
    height: 100%;
    background: linear-gradient(90deg, var(--success-color), var(--secondary-color));
    width: 0%;
    transition: width 0.5s ease;
    display: flex;
    align-items: center;
    justify-content: center;
    position: relative;
}

.progress-text {
    color: white;
    font-weight: 700;
    position: absolute;
    left: 50%;
    transform: translateX(-50%);
    z-index: 10;
    text-shadow: 0 1px 2px rgba(0, 0, 0, 0.2);
}

.level-badges {
    display: flex;
    justify-content: center;
    gap: var(--spacing-md);
    flex-wrap: wrap;
}

.badge {
    background: var(--bg-card);
    padding: var(--spacing-md);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-sm);
    text-align: center;
    min-width: 150px;
    transition: var(--transition);
    border: 3px solid transparent;
}

.badge i {
    font-size: 2rem;
    margin-bottom: var(--spacing-xs);
    display: block;
}

.badge span {
    display: block;
    font-weight: 700;
    margin-bottom: var(--spacing-xs);
}

.badge small {
    color: var(--text-gray);
    font-size: 0.85rem;
}

.badge.active {
    border-color: var(--success-color);
    transform: scale(1.05);
}

#badge-beginner i { color: var(--success-color); }
#badge-intermediate i { color: var(--orange-color); }
#badge-advanced i { color: var(--primary-color); }

/* ==========================================
   LESSONS SECTION
   ========================================== */

.lessons-section {
    background: var(--bg-light);
    padding: var(--spacing-xl) 0;
}

.level-group {
    margin-bottom: var(--spacing-xl);
}

.level-header {
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    margin-bottom: var(--spacing-lg);
    padding: var(--spacing-md);
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-md);
}

.level-header i {
    font-size: 2rem;
}

.level-header h3 {
    font-size: 1.8rem;
    font-weight: 700;
}

.lessons-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: var(--spacing-md);
}

.lesson-card {
    background: var(--bg-card);
    border-radius: var(--radius-lg);
    padding: var(--spacing-md);
    box-shadow: var(--shadow-sm);
    transition: var(--transition);
    cursor: pointer;
    position: relative;
    overflow: hidden;
}

.lesson-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 4px;
    background: linear-gradient(90deg, var(--primary-color), var(--secondary-color));
    transform: scaleX(0);
    transition: transform 0.3s ease;
}

.lesson-card:hover::before {
    transform: scaleX(1);
}

.lesson-card:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-hover);
}

.lesson-card.completed {
    border: 2px solid var(--success-color);
}

.lesson-card.completed::after {
    content: '✓';
    position: absolute;
    top: 10px;
    right: 10px;
    width: 30px;
    height: 30px;
    background: var(--success-color);
    color: white;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 700;
}

.lesson-number {
    display: inline-block;
    background: linear-gradient(135deg, var(--purple-color), var(--primary-color));
    color: white;
    padding: var(--spacing-xs) var(--spacing-md);
    border-radius: var(--radius-full);
    font-weight: 700;
    font-size: 0.85rem;
    margin-bottom: var(--spacing-sm);
}

.lesson-icon {
    font-size: 2.5rem;
    text-align: center;
    margin-bottom: var(--spacing-sm);
    color: var(--secondary-color);
}

.lesson-title {
    font-size: 1.2rem;
    font-weight: 700;
    margin-bottom: var(--spacing-xs);
    color: var(--text-dark);
}

.lesson-desc {
    color: var(--text-gray);
    font-size: 0.95rem;
    margin-bottom: var(--spacing-sm);
    line-height: 1.5;
}

.lesson-tags {
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing-xs);
    margin-bottom: var(--spacing-md);
}

.tag {
    background: var(--accent-color);
    color: var(--text-dark);
    padding: 4px 12px;
    border-radius: var(--radius-full);
    font-size: 0.75rem;
    font-weight: 600;
}

.btn-lesson {
    width: 100%;
    padding: var(--spacing-sm);
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    border: none;
    border-radius: var(--radius-md);
    font-weight: 700;
    font-size: 1rem;
    cursor: pointer;
    transition: var(--transition);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-xs);
}

.btn-lesson:hover {
    transform: scale(1.02);
    box-shadow: var(--shadow-md);
}

/* ==========================================
   FOOTER
   ========================================== */

.footer {
    background: var(--text-dark);
    color: white;
    text-align: center;
    padding: var(--spacing-lg) 0;
}

.footer p {
    margin-bottom: var(--spacing-xs);
    opacity: 0.9;
}

/* ==========================================
   RESPONSIVE DESIGN
   ========================================== */

@media (max-width: 768px) {
    body {
        padding-top: 70px;
    }
    
    .nav-menu {
        display: none;
        position: absolute;
        top: 100%;
        left: 0;
        right: 0;
        background: var(--bg-white);
        flex-direction: column;
        padding: var(--spacing-md);
        box-shadow: var(--shadow-md);
    }
    
    .nav-menu.active {
        display: flex;
    }
    
    .nav-toggle {
        display: block;
    }
    
    .hero-title {
        font-size: 2rem;
    }
    
    .hero-subtitle {
        font-size: 1.2rem;
    }
    
    .hero-stats {
        gap: var(--spacing-sm);
    }
    
    .stat-box {
        min-width: 120px;
        padding: var(--spacing-sm);
    }
    
    .stat-number {
        font-size: 2rem;
    }
    
    .section-title {
        font-size: 2rem;
    }
    
    .level-header h3 {
        font-size: 1.3rem;
    }
    
    .lessons-grid {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 480px) {
    .logo {
        font-size: 1.2rem;
    }
    
    .logo i {
        font-size: 1.5rem;
    }
    
    .hero-title {
        font-size: 1.8rem;
    }
    
    .section-title {
        font-size: 1.8rem;
    }
    
    .btn-primary {
        padding: var(--spacing-sm) var(--spacing-lg);
        font-size: 1rem;
    }
}

/* ==========================================
   ANIMATIONS
   ========================================== */

@keyframes fadeIn {
    from {
        opacity: 0;
    }
    to {
        opacity: 1;
    }
}

@keyframes slideInUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.lesson-card {
    animation: fadeIn 0.5s ease;
}

/* ==========================================
   UTILITY CLASSES
   ========================================== */

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

.mt-1 { margin-top: var(--spacing-sm); }
.mt-2 { margin-top: var(--spacing-md); }
.mt-3 { margin-top: var(--spacing-lg); }

.mb-1 { margin-bottom: var(--spacing-sm); }
.mb-2 { margin-bottom: var(--spacing-md); }
.mb-3 { margin-bottom: var(--spacing-lg); }

.p-1 { padding: var(--spacing-sm); }
.p-2 { padding: var(--spacing-md); }
.p-3 { padding: var(--spacing-lg); }