/* Custom Styles for GrandGuru */

/* ============================================
   MODERN DESIGN SYSTEM - Best Practices
   ============================================ */

:root {
    /* Enhanced Color Palette with Better Contrast */
    --primary-50: #f0f4ff;
    --primary-100: #e0e9ff;
    --primary-200: #c7d7fe;
    --primary-300: #a4bcfd;
    --primary-400: #8099fa;
    --primary-500: #667eea;
    --primary-600: #5568d3;
    --primary-700: #4652b8;
    --primary-800: #3a4394;
    --primary-900: #323a78;
    
    --secondary-500: #764ba2;
    --success-500: #10b981;
    --info-500: #3b82f6;
    --warning-500: #f59e0b;
    --danger-500: #ef4444;
    
    /* Neutral Colors */
    --gray-50: #f9fafb;
    --gray-100: #f3f4f6;
    --gray-200: #e5e7eb;
    --gray-300: #d1d5db;
    --gray-400: #9ca3af;
    --gray-500: #6b7280;
    --gray-600: #4b5563;
    --gray-700: #374151;
    --gray-800: #1f2937;
    --gray-900: #111827;
    
    /* Semantic Colors */
    --color-background: #ffffff;
    --color-surface: #f9fafb;
    --color-border: #e5e7eb;
    --color-text-primary: #1f2937;
    --color-text-secondary: #4b5563;
    --color-text-disabled: #9ca3af;
    
    /* Modern Gradients */
    --gradient-primary: linear-gradient(135deg, var(--primary-500) 0%, var(--secondary-500) 100%);
    --gradient-hero: linear-gradient(135deg, rgba(102, 126, 234, 0.95) 0%, rgba(118, 75, 162, 0.95) 100%);
    --gradient-card: linear-gradient(145deg, rgba(255,255,255,0.05) 0%, rgba(255,255,255,0.01) 100%);
    --gradient-glass: linear-gradient(135deg, rgba(255,255,255,0.1) 0%, rgba(255,255,255,0.05) 100%);
    
    /* Typography System */
    --font-family-base: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    --font-family-mono: 'SF Mono', 'Monaco', 'Cascadia Code', 'Consolas', 'Courier New', monospace;
    
    --font-size-xs: 0.75rem;     /* 12px */
    --font-size-sm: 0.875rem;    /* 14px */
    --font-size-base: 1rem;      /* 16px */
    --font-size-lg: 1.125rem;    /* 18px */
    --font-size-xl: 1.25rem;     /* 20px */
    --font-size-2xl: 1.5rem;     /* 24px */
    --font-size-3xl: 1.875rem;   /* 30px */
    --font-size-4xl: 2.25rem;    /* 36px */
    --font-size-5xl: 3rem;       /* 48px */
    
    --font-weight-light: 300;
    --font-weight-normal: 400;
    --font-weight-medium: 500;
    --font-weight-semibold: 600;
    --font-weight-bold: 700;
    
    --line-height-tight: 1.25;
    --line-height-normal: 1.5;
    --line-height-relaxed: 1.625;
    --line-height-loose: 2;
    
    --letter-spacing-tight: -0.025em;
    --letter-spacing-normal: 0;
    --letter-spacing-wide: 0.025em;
    
    /* Spacing Scale (8px base) */
    --spacing-0: 0;
    --spacing-1: 0.25rem;   /* 4px */
    --spacing-2: 0.5rem;    /* 8px */
    --spacing-3: 0.75rem;   /* 12px */
    --spacing-4: 1rem;      /* 16px */
    --spacing-5: 1.25rem;   /* 20px */
    --spacing-6: 1.5rem;    /* 24px */
    --spacing-8: 2rem;      /* 32px */
    --spacing-10: 2.5rem;   /* 40px */
    --spacing-12: 3rem;     /* 48px */
    --spacing-16: 4rem;     /* 64px */
    --spacing-20: 5rem;     /* 80px */
    --spacing-24: 6rem;     /* 96px */
    
    /* Modern Shadows */
    --shadow-xs: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-sm: 0 1px 3px 0 rgba(0, 0, 0, 0.1), 0 1px 2px 0 rgba(0, 0, 0, 0.06);
    --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);
    --shadow-2xl: 0 25px 50px -12px rgba(0, 0, 0, 0.25);
    --shadow-inner: inset 0 2px 4px 0 rgba(0, 0, 0, 0.06);
    
    /* Border Radius */
    --radius-none: 0;
    --radius-sm: 0.25rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --radius-xl: 1rem;
    --radius-2xl: 1.5rem;
    --radius-full: 9999px;
    
    /* Transitions */
    --transition-fast: 150ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-base: 250ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-slow: 350ms cubic-bezier(0.4, 0, 0.2, 1);
    
    /* Z-Index Scale */
    --z-dropdown: 1000;
    --z-sticky: 1020;
    --z-fixed: 1030;
    --z-modal-backdrop: 1040;
    --z-modal: 1050;
    --z-popover: 1060;
    --z-tooltip: 1070;
    
    /* Content Max Width */
    --max-width-sm: 640px;
    --max-width-md: 768px;
    --max-width-lg: 1024px;
    --max-width-xl: 1280px;
    --max-width-2xl: 1536px;
    --max-width-prose: 65ch;
    
    /* Code Block Colors */
    --code-bg: #1e1e1e;
    --code-header-bg: #2d2d2d;
    --code-text: #d4d4d4;
    --code-border: #3e3e3e;
    --code-comment: #6a9955;
    --code-keyword: #569cd6;
    --code-string: #ce9178;
}

/* ============================================
   GLOBAL STYLES & RESET
   ============================================ */

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

html {
    font-size: 16px;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-family-base);
    font-size: var(--font-size-base);
    line-height: var(--line-height-normal);
    color: var(--color-text-primary);
    background-color: #ffffff;
    min-height: 100vh;
}

/* Enhanced Typography */
h1, h2, h3, h4, h5, h6 {
    font-weight: var(--font-weight-bold);
    line-height: var(--line-height-tight);
    letter-spacing: var(--letter-spacing-tight);
    margin-bottom: var(--spacing-4);
    color: #111827 !important;
}

h1 {
    font-size: var(--font-size-4xl);
    font-weight: var(--font-weight-bold);
}

h2 {
    font-size: var(--font-size-3xl);
}

h3 {
    font-size: var(--font-size-2xl);
}

h4 {
    font-size: var(--font-size-xl);
}

h5 {
    font-size: var(--font-size-lg);
}

h6 {
    font-size: var(--font-size-base);
}

p {
    margin-bottom: var(--spacing-4);
    line-height: var(--line-height-relaxed);
    color: #1f2937;
}

a {
    color: var(--primary-500);
    text-decoration: none;
    transition: color var(--transition-fast);
}

a:hover {
    color: var(--primary-600);
}

/* Focus States for Accessibility */
:focus-visible {
    outline: 2px solid var(--primary-500);
    outline-offset: 2px;
    border-radius: var(--radius-sm);
}

/* Selection */
::selection {
    background-color: var(--primary-200);
    color: var(--primary-900);
}

/* Scrollbar Styling */
::-webkit-scrollbar {
    width: 12px;
    height: 12px;
}

::-webkit-scrollbar-track {
    background: var(--gray-100);
}

::-webkit-scrollbar-thumb {
    background: var(--gray-300);
    border-radius: var(--radius-full);
    border: 2px solid var(--gray-100);
}

::-webkit-scrollbar-thumb:hover {
    background: var(--gray-400);
}

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

.breadcrumb {
    background: transparent;
    padding: var(--spacing-3) 0;
}

.breadcrumb-item {
    font-size: var(--font-size-sm);
}

.breadcrumb-item a {
    color: var(--primary-600);
    text-decoration: none;
    font-weight: var(--font-weight-medium);
}

.breadcrumb-item a:hover {
    color: var(--primary-700);
    text-decoration: underline;
}

.breadcrumb-item.active {
    color: #6b7280;
    font-weight: var(--font-weight-normal);
}

.container-prose {
    max-width: var(--max-width-prose);
    margin: 0 auto;
}

.text-balance {
    text-wrap: balance;
}

.sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border-width: 0;
}

main {
    flex: 1;
}

/* Navbar */
.navbar-brand {
    font-weight: bold;
    font-size: 1.5rem;
}

/* Cards */
.card {
    transition: transform 0.2s, box-shadow 0.2s;
}

.card:hover {
    transform: translateY(-5px);
    box-shadow: 0 4px 15px rgba(0,0,0,0.1);
}

.hover-shadow:hover {
    box-shadow: 0 4px 15px rgba(0,0,0,0.15);
}

/* Course Cards */
.course-card {
    border: none;
    border-radius: 10px;
    overflow: hidden;
}

.course-card .card-img-top {
    height: 200px;
    object-fit: cover;
}

/* Buttons - Premium Style */
.btn {
    border-radius: var(--radius-lg);
    padding: var(--spacing-3) var(--spacing-6);
    font-weight: var(--font-weight-semibold);
    transition: all var(--transition-base);
    border: none;
    position: relative;
    overflow: hidden;
}

.btn::before {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 0;
    height: 0;
    border-radius: 50%;
    background: rgba(255, 255, 255, 0.2);
    transform: translate(-50%, -50%);
    transition: width 0.6s, height 0.6s;
}

.btn:hover::before {
    width: 300px;
    height: 300px;
}

.btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 20px rgba(0,0,0,0.15);
}

.btn-primary {
    background: var(--gradient-primary);
    box-shadow: 0 4px 12px rgba(102, 126, 234, 0.3);
}

.btn-primary:hover {
    box-shadow: 0 8px 24px rgba(102, 126, 234, 0.4);
}

.btn-outline-primary {
    border: 2px solid transparent;
    background: linear-gradient(white, white) padding-box,
                var(--gradient-primary) border-box;
    color: #667eea;
}

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

/* Badges */
.badge {
    padding: 0.4rem 0.8rem;
    font-weight: 500;
    border-radius: var(--radius-md);
}

/* Accordion */
.accordion-button {
    color: #111827 !important;
    font-weight: var(--font-weight-semibold);
}

.accordion-button:not(.collapsed) {
    background-color: var(--primary-color);
    color: #111827 !important;
}

.accordion-button:focus {
    box-shadow: none;
    border-color: var(--primary-color);
}

.accordion-button strong {
    color: #111827 !important;
}

/* Footer */
footer {
    margin-top: auto;
}

footer a {
    text-decoration: none;
    transition: opacity 0.2s;
}

footer a:hover {
    opacity: 0.8;
}

/* Admin Styles */
.sidebar {
    box-shadow: 2px 0 5px rgba(0,0,0,0.1);
}

.sidebar .nav-link {
    padding: 0.75rem 1rem;
    transition: all 0.2s;
    border-radius: 5px;
    margin: 0.2rem 0.5rem;
}

.sidebar-heading {
    font-size: 0.75rem;
    text-transform: uppercase;
}

/* Animations */
@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.fade-in {
    animation: fadeIn 0.5s ease-in;
}

/* Responsive */
@media (max-width: 768px) {
    .display-4 {
        font-size: 2rem;
    }
    
    .lead {
        font-size: 1rem;
    }
}

/* Loading Spinner */
.spinner-container {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 300px;
}

/* Alert Improvements */
.alert {
    border-radius: 8px;
    border: none;
}

/* Table Improvements */
.table {
    border-radius: 8px;
    overflow: hidden;
}

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

/* Form Improvements */
.form-control:focus,
.form-select:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 0.2rem rgba(13, 110, 253, 0.25);
}

/* Category Cards */
.category-card {
    transition: all 0.3s;
    cursor: pointer;
}

.category-card:hover {
    background-color: #f8f9fa;
    transform: scale(1.05);
}

/* Language Switcher */
.language-flag {
    width: 24px;
    height: 16px;
    margin-right: 8px;
}

/* Breadcrumb */
.breadcrumb {
    background-color: transparent;
    padding: 0.5rem 0;
}

/* Lesson Content */
.lesson-content {
    line-height: 1.8;
}

.lesson-content .text-block {
    margin-bottom: 1rem;
}

.lesson-content .text-block p {
    margin-bottom: 0.75rem;
    line-height: 1.8;
}

.lesson-content .text-block ul,
.lesson-content .text-block ol {
    margin-bottom: 1rem;
    padding-left: 2rem;
}

.lesson-content .text-block li {
    margin-bottom: 0.5rem;
}

.lesson-content pre {
    background-color: #f8f9fa;
    padding: 1rem;
    border-radius: 5px;
    border-left: 4px solid var(--primary-color);
}

.lesson-content code {
    background-color: #f8f9fa;
    padding: 0.2rem 0.4rem;
    border-radius: 3px;
    color: #d63384;
}

/* Lesson Content Tables */
.lesson-content table {
    width: 100%;
    margin: 1.5rem 0;
    border-collapse: collapse;
    border: 2px solid #dee2e6;
    background: white;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

.lesson-content table th {
    background: linear-gradient(135deg, #0d6efd 0%, #0a58ca 100%);
    color: white;
    font-weight: 600;
    padding: 0.875rem 1rem;
    text-align: left;
    border: 1px solid #0a58ca;
    font-size: 0.95rem;
    text-transform: none;
}

.lesson-content table td {
    padding: 0.75rem 1rem;
    border: 1px solid #dee2e6;
    font-size: 0.95rem;
    vertical-align: top;
}

.lesson-content table tbody tr:nth-child(even) {
    background: #f8f9fa;
}

.lesson-content table tbody tr:hover {
    background: #e9ecef;
    transition: background 0.2s ease;
}

/* Для мобильных устройств - горизонтальная прокрутка */
@media (max-width: 768px) {
    .lesson-content table {
        display: block;
        overflow-x: auto;
        white-space: nowrap;
    }
    
    .lesson-content table th,
    .lesson-content table td {
        padding: 0.5rem 0.75rem;
        font-size: 0.875rem;
    }
}

/* Progress Bar */
.course-progress {
    height: 8px;
    border-radius: 10px;
    background-color: #e9ecef;
}

.course-progress .progress-bar {
    border-radius: 10px;
}

/* ============================================
   COURSE CARD - Premium Modern Design
   ============================================ */
.course-card {
    height: 100%;
    border: none;
    border-radius: var(--radius-2xl);
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.08);
    transition: all var(--transition-base);
    background: white;
    overflow: hidden;
    position: relative;
    display: flex;
    flex-direction: column;
}

.course-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 5px;
    background: var(--gradient-primary);
    transform: scaleX(0);
    transform-origin: left;
    transition: transform var(--transition-base);
}

.course-card:hover {
    transform: translateY(-12px);
    box-shadow: 0 20px 40px rgba(102, 126, 234, 0.15), 0 10px 20px rgba(0, 0, 0, 0.1);
}

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

.course-card .card-body {
    padding: var(--spacing-8);
    display: flex;
    flex-direction: column;
    flex-grow: 1;
}

.course-card .card-title {
    font-size: 1.375rem;
    font-weight: var(--font-weight-bold);
    color: #111827;
    margin-bottom: var(--spacing-4);
    line-height: 1.3;
    min-height: 2.6em;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    line-clamp: 2;
    -webkit-box-orient: vertical;
    overflow: hidden;
}

.course-card .card-text {
    color: #6b7280;
    line-height: 1.6;
    margin-bottom: var(--spacing-6);
    font-size: 0.9375rem;
    flex-grow: 1;
    display: -webkit-box;
    -webkit-line-clamp: 3;
    line-clamp: 3;
    -webkit-box-orient: vertical;
    overflow: hidden;
}

.course-card .card-footer {
    background: transparent;
    border: none;
    padding: 0 var(--spacing-8) var(--spacing-6);
}

.course-card .btn {
    width: 100%;
    font-weight: var(--font-weight-semibold);
    border-radius: var(--radius-lg);
    padding: var(--spacing-2) var(--spacing-4);
    transition: all var(--transition-fast);
    font-size: 0.875rem;
}

.course-card .btn-primary {
    background: var(--gradient-primary);
    border: none;
    box-shadow: 0 4px 12px rgba(102, 126, 234, 0.3);
}

.course-card .btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(102, 126, 234, 0.4);
}

.badge-featured {
    background: linear-gradient(135deg, #f093fb 0%, #f5576c 100%);
    color: white;
    padding: var(--spacing-2) var(--spacing-4);
    font-weight: var(--font-weight-bold);
    font-size: 0.75rem;
    border-radius: var(--radius-md);
    box-shadow: 0 4px 12px rgba(245, 87, 108, 0.3);
    letter-spacing: 0.5px;
    text-transform: uppercase;
}

.course-card .badge {
    font-size: 0.8125rem;
    padding: var(--spacing-2) var(--spacing-4);
    border-radius: var(--radius-md);
    font-weight: var(--font-weight-semibold);
}

.course-card .badge.bg-primary {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%) !important;
    border: none;
}

/* Course Card Meta Info */
.course-card-meta {
    display: flex;
    gap: var(--spacing-3);
    margin-top: var(--spacing-4);
    padding-top: var(--spacing-4);
    border-top: 1px solid #f3f4f6;
}

.course-card-meta-item {
    display: flex;
    align-items: center;
    gap: var(--spacing-2);
    color: #6b7280;
    font-size: 0.875rem;
}

.course-card-meta-item i {
    color: var(--primary-500);
}

/* ============================================
   FEATURES SECTION - Modern Design
   ============================================ */
.features-section {
    padding: var(--spacing-20) 0;
    background: linear-gradient(180deg, var(--gray-50) 0%, white 100%);
}

.features-section h2 {
    text-align: center;
    margin-bottom: var(--spacing-12);
    color: var(--color-text-primary);
    font-weight: var(--font-weight-bold);
    font-size: var(--font-size-4xl);
    position: relative;
    display: inline-block;
    left: 50%;
    transform: translateX(-50%);
}

.features-section h2::after {
    content: '';
    position: absolute;
    bottom: -12px;
    left: 50%;
    transform: translateX(-50%);
    width: 60px;
    height: 4px;
    background: var(--gradient-primary);
    border-radius: var(--radius-full);
}

.feature-card {
    text-align: center;
    padding: var(--spacing-10);
    background: white;
    border-radius: var(--radius-2xl);
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.02);
    transition: all var(--transition-base);
    height: 100%;
    border: 1px solid transparent;
    position: relative;
    overflow: hidden;
    display: flex;
    flex-direction: column;
    align-items: center;
}

.feature-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 4px;
    background: var(--gradient-primary);
    transform: scaleX(0);
    transition: transform var(--transition-base);
}

.feature-card:hover {
    transform: translateY(-10px);
    box-shadow: 
        0 20px 40px rgba(102, 126, 234, 0.15),
        0 0 0 1px rgba(102, 126, 234, 0.1);
    border-color: rgba(102, 126, 234, 0.1);
}

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

.feature-card > * {
    position: relative;
    z-index: 1;
}

.feature-card i {
    font-size: 3.5rem;
    background: var(--gradient-primary);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: var(--spacing-6);
    display: inline-block;
    transition: all var(--transition-base);
}

.feature-card:hover i {
    transform: scale(1.1) rotate(5deg);
}

.feature-card h3 {
    margin-bottom: var(--spacing-4);
    color: #1f2937;
    font-size: 1.5rem;
    font-weight: var(--font-weight-bold);
    letter-spacing: -0.01em;
}

.feature-card p {
    color: #4b5563;
    line-height: var(--line-height-relaxed);
    margin-bottom: 0;
    font-size: var(--font-size-base);
    flex-grow: 1;
}

/* ============================================
   FEATURES SECTION ENDS HERE
   ============================================ */

/* ============================================
   NAVBAR - Premium Design
   ============================================ */
.navbar-gradient {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%) !important;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
}

.navbar-gradient .navbar-brand {
    color: white !important;
    font-weight: var(--font-weight-bold);
    font-size: var(--font-size-xl);
    letter-spacing: var(--letter-spacing-tight);
    transition: transform var(--transition-fast);
}

.navbar-gradient .navbar-brand:hover {
    transform: translateY(-2px);
}

.navbar-gradient .nav-link {
    color: white !important;
    font-weight: var(--font-weight-semibold);
    padding: var(--spacing-2) var(--spacing-4);
    margin: 0 var(--spacing-1);
    border-radius: var(--radius-md);
    transition: all var(--transition-fast);
    position: relative;
    text-shadow: 0 1px 2px rgba(0, 0, 0, 0.1);
}

.navbar-gradient .nav-link::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 50%;
    width: 0;
    height: 2px;
    background: white;
    transform: translateX(-50%);
    transition: width var(--transition-fast);
}

.navbar-gradient .nav-link:hover {
    background: rgba(255, 255, 255, 0.1);
    color: white !important;
}

.navbar-gradient .nav-link:hover::after {
    width: 80%;
}

.navbar-gradient .navbar-toggler {
    border-color: rgba(255, 255, 255, 0.3);
    border-width: 2px;
    border-radius: var(--radius-md);
}

.navbar-gradient .navbar-toggler:focus {
    box-shadow: 0 0 0 3px rgba(255, 255, 255, 0.2);
}

.navbar-gradient .navbar-toggler-icon {
    background-image: url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 30 30'%3e%3cpath stroke='rgba(255, 255, 255, 0.95)' stroke-linecap='round' stroke-miterlimit='10' stroke-width='2' d='M4 7h22M4 15h22M4 23h22'/%3e%3c/svg%3e");
    width: 24px;
    height: 24px;
}

/* Dropdown Menu */
.navbar-gradient .dropdown-menu {
    background: white;
    border: none;
    box-shadow: var(--shadow-lg);
    border-radius: var(--radius-lg);
    padding: var(--spacing-2);
    margin-top: var(--spacing-2);
    animation: dropdownFade 0.2s ease-out;
}

@keyframes dropdownFade {
    from {
        opacity: 0;
        transform: translateY(-10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.navbar-gradient .dropdown-item {
    border-radius: var(--radius-md);
    padding: var(--spacing-2) var(--spacing-4);
    color: var(--color-text-primary);
    font-weight: var(--font-weight-medium);
    transition: all var(--transition-fast);
}

.navbar-gradient .dropdown-item:hover {
    background: var(--gray-100);
    color: var(--primary-600);
    transform: translateX(4px);
}

.navbar-gradient .dropdown-item.active {
    background: var(--primary-100);
    color: var(--primary-700);
}

/* ============================================
   HERO SECTION - Premium Design with Particles
   ============================================ */
.hero-section {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
    padding: clamp(4rem, 12vw, 8rem) 0;
    text-align: center;
    margin-bottom: var(--spacing-16);
    position: relative;
    overflow: hidden;
}

.hero-section::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: 
        radial-gradient(circle at 20% 30%, rgba(255,255,255,0.15) 0%, transparent 50%),
        radial-gradient(circle at 80% 70%, rgba(255,255,255,0.1) 0%, transparent 50%),
        radial-gradient(circle at 50% 50%, rgba(255,255,255,0.05) 0%, transparent 70%);
    pointer-events: none;
}

.hero-section::after {
    content: '';
    position: absolute;
    bottom: -2px;
    left: 0;
    right: 0;
    height: 100px;
    background: linear-gradient(180deg, transparent 0%, white 100%);
}

.hero-section > .container {
    position: relative;
    z-index: 1;
}

.hero-section h1 {
    font-size: clamp(2rem, 5vw, 3.5rem);
    font-weight: var(--font-weight-bold);
    margin-bottom: var(--spacing-6);
    text-shadow: 0 2px 30px rgba(0, 0, 0, 0.15);
    letter-spacing: -0.02em;
    animation: fadeInUp 0.8s ease-out;
    line-height: 1.15;
}

.hero-section p {
    font-size: clamp(1rem, 2vw, 1.25rem);
    margin-bottom: var(--spacing-8);
    opacity: 0.95;
    font-weight: var(--font-weight-normal);
    line-height: var(--line-height-relaxed);
    max-width: 650px;
    margin-left: auto;
    margin-right: auto;
    animation: fadeInUp 0.8s ease-out 0.2s both;
}

.hero-section .btn {
    padding: var(--spacing-4) var(--spacing-10);
    font-size: var(--font-size-lg);
    font-weight: var(--font-weight-bold);
    border-radius: var(--radius-full);
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.2);
    transition: all var(--transition-base);
    animation: fadeInUp 0.8s ease-out 0.4s both;
    border: 2px solid rgba(255, 255, 255, 0.2);
    backdrop-filter: blur(10px);
}

.hero-section .btn:hover {
    transform: translateY(-4px) scale(1.02);
    box-shadow: 0 15px 40px rgba(0, 0, 0, 0.3);
    border-color: rgba(255, 255, 255, 0.4);
}

@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(40px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* ============================================
   FEATURES SECTION COMPONENT
   ============================================ */
.features-section {
    padding: var(--spacing-xxl) 0;
    background-color: var(--light-color);
}

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

.feature-card {
    text-align: center;
    padding: var(--spacing-xl);
    background: white;
    border-radius: var(--border-radius-lg);
    box-shadow: var(--box-shadow);
    transition: var(--transition);
    height: 100%;
}

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

.feature-card i {
    font-size: 3rem;
    color: var(--primary-color);
    margin-bottom: var(--spacing-md);
}

.feature-card h3 {
    margin-bottom: var(--spacing-md);
    color: var(--dark-color);
}

/* ============================================
   CODE BLOCK - Premium Design with Line Numbers
   ============================================ */
.code-block {
    border-radius: var(--radius-2xl);
    overflow: hidden;
    background: #1e293b;
    margin-bottom: var(--spacing-8);
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.15);
    border: 1px solid #334155;
}

.code-header {
    background: linear-gradient(135deg, #1e293b 0%, #0f172a 100%);
    color: #fff;
    padding: var(--spacing-4) var(--spacing-6);
    font-size: var(--font-size-sm);
    border-bottom: 1px solid #334155;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.code-language {
    text-transform: uppercase;
    font-weight: var(--font-weight-bold);
    color: #60a5fa;
    letter-spacing: 0.1em;
    font-size: var(--font-size-sm);
}

.copy-btn {
    font-size: var(--font-size-sm);
    padding: var(--spacing-2) var(--spacing-5);
    background: rgba(96, 165, 250, 0.1);
    border: 1px solid rgba(96, 165, 250, 0.3);
    color: #60a5fa;
    border-radius: var(--radius-lg);
    transition: all var(--transition-fast);
    font-weight: var(--font-weight-semibold);
    cursor: pointer;
}

.copy-btn:hover {
    background: rgba(96, 165, 250, 0.2);
    border-color: rgba(96, 165, 250, 0.5);
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(96, 165, 250, 0.2);
}

.copy-btn:active {
    transform: translateY(0);
}

.code-block pre {
    margin: 0;
    padding: var(--spacing-6);
    background: #1e293b;
    color: #e2e8f0;
    overflow-x: auto;
    line-height: 1.7;
}

.code-block code {
    font-family: var(--font-family-mono);
    font-size: 0.95rem;
    line-height: 1.7;
}

/* ============================================
   QUIZ BLOCK - Premium Interactive Design
   ============================================ */
.quiz-block {
    border: none;
    border-radius: var(--radius-2xl);
    overflow: hidden;
    background: white;
    margin-bottom: var(--spacing-10);
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.08);
    transition: all var(--transition-base);
}

.quiz-block:hover {
    box-shadow: 0 12px 32px rgba(0, 0, 0, 0.12);
    transform: translateY(-4px);
}

.quiz-header {
    background: var(--gradient-primary);
    color: white;
    padding: var(--spacing-6) var(--spacing-8);
    font-weight: var(--font-weight-bold);
    font-size: 1.25rem;
    display: flex;
    align-items: center;
    gap: var(--spacing-3);
}

.quiz-header i {
    font-size: 1.5rem;
}

.quiz-body {
    padding: var(--spacing-8);
}

.quiz-question {
    font-size: 1.25rem;
    font-weight: var(--font-weight-bold);
    margin-bottom: var(--spacing-8);
    color: #1f2937;
    line-height: var(--line-height-relaxed);
    letter-spacing: -0.01em;
}

.quiz-options {
    margin-bottom: var(--spacing-6);
}

.quiz-option {
    /* layout: left area for checkbox (44px) + flexible text column */
    display: grid;
    grid-template-columns: 44px 1fr;
    align-items: center;
    gap: var(--spacing-4);
    padding: var(--spacing-5) var(--spacing-6);
    margin-bottom: var(--spacing-4);
    border: 2px solid #e5e7eb;
    border-radius: var(--radius-xl);
    background: #f9fafb;
    transition: all var(--transition-fast);
    cursor: pointer;
    position: relative;
    font-size: var(--font-size-base);
    font-weight: var(--font-weight-medium);
}

.quiz-option:hover {
    background: rgba(102, 126, 234, 0.05);
    border-color: rgba(102, 126, 234, 0.3);
    transform: translateX(4px);
}

.quiz-option .form-check-input {
    cursor: pointer;
    width: 22px;
    height: 22px;
    margin: 0;
    justify-self: center;
    align-self: center;
    border-radius: 6px; /* slightly rounded square */
    border: 2px solid #d1d5db;
    background-color: #ffffff;
    box-shadow: 0 1px 0 rgba(16,24,40,0.03) inset;
}

.quiz-option .form-check-input:checked {
    background-color: #667eea;
    border-color: #667eea;
    background-image: url("data:image/svg+xml,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 16 16'%3e%3cpath fill='white' d='M12.207 4.793a1 1 0 010 1.414l-5 5a1 1 0 01-1.414 0l-2-2a1 1 0 011.414-1.414L6.5 9.086l4.293-4.293a1 1 0 011.414 0z'/%3e%3c/svg%3e");
}

.quiz-option .form-check-label {
    cursor: pointer;
    font-size: var(--font-size-base);
    line-height: var(--line-height-relaxed);
    color: #1f2937;
    margin: 0;
    font-weight: var(--font-weight-normal);
}

.quiz-option.correct {
    background: linear-gradient(135deg, #d1fae5 0%, #a7f3d0 100%);
    border-color: var(--success-500);
    box-shadow: 0 0 0 4px rgba(16, 185, 129, 0.1);
}

.quiz-option.incorrect {
    background: linear-gradient(135deg, #fee2e2 0%, #fecaca 100%);
    border-color: var(--danger-500);
    box-shadow: 0 0 0 4px rgba(239, 68, 68, 0.1);
}

.quiz-actions {
    display: flex;
    gap: var(--spacing-3);
    margin-top: var(--spacing-4);
}

.quiz-result {
    padding: var(--spacing-4);
    border-radius: var(--radius-lg);
    font-weight: var(--font-weight-medium);
    margin-top: var(--spacing-4);
    display: flex;
    align-items: center;
    gap: var(--spacing-2);
}

.quiz-result i {
    font-size: var(--font-size-xl);
}

.quiz-result.correct {
    background: linear-gradient(135deg, #d1fae5 0%, #a7f3d0 100%);
    color: #065f46;
    border: 2px solid var(--success-500);
}

.quiz-result.incorrect {
    background: linear-gradient(135deg, #fee2e2 0%, #fecaca 100%);
    color: #991b1b;
    border: 2px solid var(--danger-500);
}

/* ============================================
   EXERCISE BLOCK - Premium Interactive Design
   ============================================ */
.exercise-block {
    border: none;
    border-radius: var(--radius-2xl);
    background: white;
    margin-bottom: var(--spacing-10);
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.08);
    transition: all var(--transition-base);
}

.exercise-block:hover {
    box-shadow: 0 12px 32px rgba(0, 0, 0, 0.12);
    transform: translateY(-4px);
}

.exercise-header {
    background: linear-gradient(135deg, #10b981 0%, #059669 100%);
    color: white;
    padding: var(--spacing-6) var(--spacing-8);
    font-weight: var(--font-weight-bold);
    font-size: 1.25rem;
    display: flex;
    align-items: center;
    gap: var(--spacing-3);
}

.exercise-header i {
    font-size: 1.5rem;
}

.exercise-body {
    padding: var(--spacing-8);
}

.exercise-task {
    font-size: 1.125rem;
    margin-bottom: var(--spacing-6);
    color: #1f2937;
    line-height: var(--line-height-relaxed);
    padding: var(--spacing-6);
    background: linear-gradient(135deg, #f0fdf4 0%, #dcfce7 100%);
    border-left: 4px solid #10b981;
    border-radius: var(--radius-xl);
    font-weight: var(--font-weight-medium);
}

.exercise-solution {
    margin-top: var(--spacing-6);
    padding: var(--spacing-6);
    background: #f9fafb;
    border: 2px solid #e5e7eb;
    border-radius: var(--radius-xl);
    animation: slideDown 0.3s ease-out;
}

@keyframes slideDown {
    from {
        opacity: 0;
        transform: translateY(-10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.exercise-solution h6 {
    color: var(--success-500);
    font-weight: var(--font-weight-semibold);
    margin-bottom: var(--spacing-3);
}

.exercise-solution pre {
    margin: 0;
    background: var(--code-bg);
    padding: var(--spacing-4);
    border-radius: var(--radius-lg);
    color: var(--code-text);
    white-space: pre-wrap;
    word-wrap: break-word;
    overflow-wrap: break-word;
    max-width: 100%;
}

.exercise-solution code {
    white-space: pre-wrap;
    word-break: break-word;
}

.solution-text {
    background: #1e1e1e;
    color: #ffffff;
    padding: 1.5rem;
    border-radius: var(--radius-lg);
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Arial, sans-serif;
    font-size: 1.1rem;
    font-weight: 400;
    line-height: 1.8;
    white-space: pre-wrap;
    word-wrap: break-word;
    overflow-wrap: break-word;
    word-break: break-word;
    margin: 0;
}

/* ============================================
   LESSON SIDEBAR - Modern Navigation
   ============================================ */
.lesson-sidebar {
    position: sticky;
    top: 80px;
    border-radius: var(--radius-xl);
    box-shadow: var(--shadow-md);
    overflow: hidden;
    transition: all var(--transition-base);
}

.lesson-sidebar:hover {
    box-shadow: var(--shadow-lg);
}

.lesson-sidebar .card-header {
    background: var(--gradient-primary);
    color: white;
    font-weight: var(--font-weight-semibold);
    padding: var(--spacing-4);
    border: none;
}

.lesson-sidebar .card-header h5 {
    margin: 0;
    font-size: var(--font-size-lg);
    color: white !important;
}

/* Card headers with colored backgrounds */
.card-header.bg-primary,
.card-header.bg-primary h1,
.card-header.bg-primary h2,
.card-header.bg-primary h3,
.card-header.bg-primary h4,
.card-header.bg-primary h5,
.card-header.bg-primary h6 {
    color: white !important;
}

.card-header.text-white h1,
.card-header.text-white h2,
.card-header.text-white h3,
.card-header.text-white h4,
.card-header.text-white h5,
.card-header.text-white h6 {
    color: white !important;
}

.lesson-sidebar .list-group-item {
    border: none;
    border-bottom: 1px solid var(--color-border);
    padding: var(--spacing-4);
    transition: all var(--transition-fast);
    position: relative;
}

.lesson-sidebar .list-group-item::before {
    content: '';
    position: absolute;
    left: 0;
    top: 0;
    bottom: 0;
    width: 3px;
    background: var(--gradient-primary);
    transform: scaleY(0);
    transition: transform var(--transition-fast);
}

.lesson-sidebar .list-group-item:hover:not(.active) {
    background-color: var(--gray-50);
    transform: translateX(8px);
}

.lesson-sidebar .list-group-item:hover:not(.active)::before {
    transform: scaleY(1);
}

.lesson-sidebar .list-group-item.active {
    background: linear-gradient(90deg, var(--primary-50) 0%, transparent 100%);
    border-color: var(--primary-200);
    color: var(--primary-700);
    font-weight: var(--font-weight-semibold);
}

.lesson-sidebar .list-group-item.active::before {
    transform: scaleY(1);
}

.lesson-sidebar .list-group-item i {
    margin-right: var(--spacing-2);
}

/* ============================================
   FOOTER - Modern Design
   ============================================ */
.footer-dark {
    background: linear-gradient(180deg, var(--gray-900) 0%, #000 100%);
    color: var(--gray-400);
    padding: var(--spacing-12) 0; /* slightly smaller padding so footer is visible without large whitespace */
    margin-top: var(--spacing-12); /* reduce excessive gap above footer */
    border-top: 1px solid var(--gray-800);
    position: relative;
    z-index: 10;
}

.footer-dark h5 {
    color: white;
    font-weight: var(--font-weight-semibold);
    margin-bottom: var(--spacing-4);
}

.footer-dark a {
    color: var(--gray-400);
    transition: color var(--transition-fast);
}

.footer-dark a:hover {
    color: white;
    text-decoration: none;
}

/* ============================================
   RESPONSIVE DESIGN - Mobile First
   ============================================ */

/* Tablet and below */
@media (max-width: 1024px) {
    :root {
        --font-size-5xl: 2.5rem;
        --font-size-4xl: 2rem;
    }
}

/* Mobile */
@media (max-width: 768px) {
    :root {
        --font-size-5xl: 2rem;
        --font-size-4xl: 1.75rem;
        --spacing-20: 3rem;
    }
    
    .hero-section {
        padding: var(--spacing-12) 0;
    }
    
    .hero-section h1 {
        font-size: var(--font-size-4xl);
    }
    
    .hero-section p {
        font-size: var(--font-size-base);
    }
    
    .lesson-sidebar {
        position: relative;
        top: 0;
        margin-bottom: var(--spacing-6);
    }
    
    .feature-card,
    .course-card {
        margin-bottom: var(--spacing-6);
    }
    
    .quiz-option:hover,
    .lesson-sidebar .list-group-item:hover:not(.active) {
        transform: translateX(4px);
    }
    
    .navbar-gradient .nav-link {
        margin: var(--spacing-1) 0;
    }
}

/* Small mobile */
@media (max-width: 480px) {
    .hero-section {
        padding: var(--spacing-10) 0;
    }
    
    .features-section {
        padding: var(--spacing-12) 0;
    }
}

/* End of styles */

/* ============================================
   LESSON CONTENT - Better Readability
   ============================================ */
.lesson-content {
    color: #1f2937;
    line-height: 1.75;
}

.lesson-content h2 {
    color: #111827;
    font-size: var(--font-size-2xl);
    font-weight: var(--font-weight-bold);
    margin-top: var(--spacing-8);
    margin-bottom: var(--spacing-4);
    line-height: var(--line-height-tight);
}

.lesson-content p {
    color: #374151;
    font-size: var(--font-size-base);
    line-height: 1.75;
    margin-bottom: var(--spacing-4);
}

.lesson-content ul, 
.lesson-content ol {
    color: #374151;
    padding-left: var(--spacing-6);
    margin-bottom: var(--spacing-4);
}

.lesson-content li {
    margin-bottom: var(--spacing-2);
    line-height: 1.75;
}

.lesson-content .alert {
    font-size: var(--font-size-base);
    padding: var(--spacing-4);
    border-radius: var(--radius-lg);
    margin-bottom: var(--spacing-4);
}

.lesson-content .alert-info {
    background-color: #dbeafe;
    border-color: #3b82f6;
    color: #1e40af;
}

.lesson-content .alert-warning {
    background-color: #fef3c7;
    border-color: #f59e0b;
    color: #92400e;
}

.lesson-content blockquote {
    border-left: 4px solid var(--primary-500);
    padding-left: var(--spacing-4);
    margin: var(--spacing-6) 0;
    font-style: italic;
    color: #4b5563;
}

/* Badges */
.badge {
    font-weight: var(--font-weight-semibold);
    padding: var(--spacing-2) var(--spacing-3);
    border-radius: var(--radius-md);
}

.badge.bg-info {
    background-color: #3b82f6 !important;
    color: white;
}

.badge.bg-secondary {
    background-color: #6b7280 !important;
    color: white;
}

/* ============================================
   UTILITY CLASSES - Display & Layout
   ============================================ */
.d-none {
    display: none !important;
}

.d-inline {
    display: inline !important;
}

.d-block {
    display: block !important;
}

/* Sticky elements */
.sticky-top-20 {
    position: sticky;
    top: 20px;
}

/* Progress bar styles */
.progress-bar-animated {
    width: 100%;
}

.progress-height-25 {
    height: 25px;
}

.progress-height-30 {
    height: 30px;
}

/* Pre/Code display styles */
.pre-wrap {
    white-space: pre-wrap !important;
}

.pre-scrollable {
    max-height: 500px;
    overflow-y: auto;
}

.code-display {
    background-color: #f8f9fa;
    padding: 15px;
    border-radius: 5px;
    white-space: pre-wrap;
    font-size: 14px;
    line-height: 1.5;
}

.code-display-small {
    display: block;
    white-space: pre-wrap;
    font-size: 11px;
}

.code-display-response {
    background-color: #f0f8ff;
    padding: 15px;
    border-radius: 5px;
    white-space: pre-wrap;
    font-size: 14px;
    line-height: 1.5;
    max-height: 500px;
    overflow-y: auto;
}

.text-scrollable {
    white-space: pre-wrap;
    max-height: 400px;
    overflow-y: auto;
}

/* ============================================
   LESSON NAVIGATION - Premium Pagination
   ============================================ */
.lesson-navigation {
    margin-top: var(--spacing-10);
    padding-top: var(--spacing-6);
    border-top: 2px solid #e5e7eb;
}

.lesson-navigation .pagination {
    gap: var(--spacing-4);
    flex-wrap: wrap;
}

.lesson-navigation .page-item {
    flex: 1;
    min-width: 150px;
}

.lesson-navigation .page-item:nth-child(2) {
    flex: 0 1 auto;
}

.lesson-navigation .page-link {
    border-radius: var(--radius-lg);
    padding: var(--spacing-4) var(--spacing-6);
    font-weight: var(--font-weight-semibold);
    border: 2px solid #e5e7eb;
    color: #1f2937;
    transition: all var(--transition-fast);
    text-align: center;
    white-space: nowrap;
}

.lesson-navigation .page-link:hover {
    background: var(--gradient-primary);
    border-color: #667eea;
    color: white;
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(102, 126, 234, 0.3);
}

.lesson-navigation .page-item.disabled .page-link {
    background: #f3f4f6;
    border-color: #e5e7eb;
    color: #9ca3af;
    cursor: not-allowed;
    opacity: 0.6;
}

.lesson-navigation .page-item.disabled .page-link:hover {
    transform: none;
    box-shadow: none;
}

@media (max-width: 768px) {
    .lesson-navigation .page-item {
        flex-basis: 100%;
    }
}