:root {
    --primary: #FF4B4B;
    --secondary: #2c3e50;
    --background: #1a1a1a;
    --card-bg: #242424;
    --text: #ffffff;
    --spacing: clamp(0.75rem, 2.5vw, 1.5rem);
    --radius: 12px;
    --transition: 0.3s ease;
}

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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: var(--background);
    color: var(--text);
    min-height: 100vh;
    position: relative;
    overflow-x: hidden;
    line-height: 1.6;
    -webkit-overflow-scrolling: touch;
}

body::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: radial-gradient(circle at 50% 50%, rgba(255, 75, 75, 0.05), transparent 50%);
    animation: backgroundPulse 10s infinite alternate;
    z-index: -1;
}

/* Header Styles with Animation */
.header {
    position: sticky;
    top: 0;
    background: rgba(26, 26, 26, 0.95);
    backdrop-filter: blur(8px);
    padding: var(--spacing);
    z-index: 1000;
    border-bottom: 1px solid rgba(255, 75, 75, 0.2);
    transition: var(--transition);
    animation: headerReveal 0.8s ease-out forwards;
}

.header.hidden {
    transform: translateY(-100%);
}

.header::before {
    content: '';
    position: absolute;
    bottom: 0;
    left: 0;
    width: 100%;
    height: 1px;
    background: linear-gradient(90deg, transparent, var(--primary), transparent);
    animation: gradientBorder 3s infinite;
}

.header-content {
    max-width: 1400px;
    margin: 0 auto;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: calc(var(--spacing) * 0.5);
    padding: 0 var(--spacing);
}

.logo-container {
    display: flex;
    align-items: center;
    gap: clamp(0.5rem, 1vw, 0.8rem);
    padding: clamp(0.5rem, 1vw, 0.75rem) clamp(0.75rem, 2vw, 1.5rem);
    background: rgba(255, 75, 75, 0.1);
    border-radius: var(--radius);
    transition: var(--transition);
}

.logo-container:hover {
    background: rgba(255, 75, 75, 0.2);
}

.logo {
    height: clamp(20px, 4vw, 35px);
    width: auto;
    transition: var(--transition);
    animation: logoPop 0.6s ease-out forwards 0.2s;
}

.brand-name {
    font-size: clamp(1rem, 2.5vw, 1.5rem);
    font-weight: 600;
    background: linear-gradient(45deg, var(--primary), #FF8F8F);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    animation: textGradient 8s linear infinite;
}

.search-container {
    width: 100%;
    padding: 0;
}

#searchInput {
    width: 100%;
    padding: clamp(0.5rem, 1.5vw, 0.75rem) 1rem;
    background: rgba(255, 255, 255, 0.05);
    border: 1px solid rgba(255, 75, 75, 0.2);
    border-radius: var(--radius);
    color: var(--text);
    font-size: clamp(0.9rem, 1.5vw, 1rem);
    transition: var(--transition);
}

#searchInput:focus {
    outline: none;
    border-color: var(--primary);
    background: rgba(255, 255, 255, 0.1);
    box-shadow: 0 0 5px rgba(255, 75, 75, 0.2);
}

/* Main Content */
.container {
    max-width: 1400px;
    margin: calc(var(--spacing) * 4) auto calc(var(--spacing) * 2);
    padding: var(--spacing);
}

.course-card {
    background: rgba(36, 36, 36, 0.8);
    border-radius: var(--radius);
    padding: var(--spacing);
    margin-bottom: var(--spacing);
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.2);
    border: 1px solid rgba(255, 255, 255, 0.1);
    backdrop-filter: blur(8px);
    position: relative;
    overflow: hidden;
    transition: var(--transition);
    animation: slideUp 0.8s var(--transition);
}

.course-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 15px 40px rgba(255, 75, 75, 0.2);
}

.course-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(90deg, transparent, rgba(255, 255, 255, 0.1), transparent);
    transition: 0.5s;
}

.course-card:hover::before {
    left: 100%;
}

.lesson-list {
    margin-top: var(--spacing);
    display: grid;
    gap: calc(var(--spacing) * 0.5);
}

.lesson {
    border-left: 4px solid var(--primary);
    padding: var(--spacing);
    background: rgba(255, 255, 255, 0.02);
    border-radius: var(--radius);
    cursor: pointer;
    transition: var(--transition);
    position: relative;
    overflow: hidden;
    animation: lessonFadeIn 0.5s ease-out;
}

.lesson::after {
    content: '→';
    position: absolute;
    right: 15px;
    top: 50%;
    transform: translateY(-50%);
    opacity: 0;
    transition: var(--transition);
}

.lesson:hover {
    background: rgba(255, 75, 75, 0.1);
    transform: translateX(3px);
}

.lesson:hover::after {
    opacity: 1;
    transform: translate(3px, -50%);
}

.lesson.active::after {
    content: '↓';
    opacity: 1;
}

.lesson-content {
    display: none;
    margin-top: var(--spacing);
    padding: var(--spacing);
    background: rgba(255, 255, 255, 0.03);
    border-radius: var(--radius);
    line-height: 1.6;
    font-size: clamp(0.9rem, 1.5vw, 1rem);
    transition: var(--transition);
}

.lesson.active .lesson-content {
    display: block;
    animation: contentReveal 0.5s ease-out forwards;
}

/* Typography */
h2 {
    font-size: clamp(1.25rem, 3vw, 2rem);
    margin-bottom: var(--spacing);
}

h3 {
    font-size: clamp(1rem, 2vw, 1.25rem);
}

.course-info {
    font-size: clamp(0.9rem, 1.5vw, 1rem);
    line-height: 1.6;
    opacity: 0.9;
    margin: var(--spacing) 0;
}

.loading {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 150px;
    font-size: clamp(1rem, 2vw, 1.2rem);
    color: var(--primary);
}

.loading::after {
    content: '...';
    animation: dots 1.5s steps(4, end) infinite;
}

/* Pagination */
.pagination {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: clamp(0.5rem, 1.5vw, 1rem);
    margin: calc(var(--spacing) * 2) 0;
    flex-wrap: wrap;
}

.pagination-btn {
    padding: clamp(0.5rem, 1.5vw, 0.75rem) 1.5rem;
    background: rgba(255, 75, 75, 0.1);
    border: 1px solid rgba(255, 75, 75, 0.2);
    border-radius: var(--radius);
    color: var(--text);
    font-size: clamp(0.9rem, 1.5vw, 1rem);
    cursor: pointer;
    transition: var(--transition);
    min-width: 100px;
}

.pagination-btn:hover {
    background: rgba(255, 75, 75, 0.2);
    transform: translateY(-2px);
}

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

.page-info {
    font-size: clamp(0.85rem, 1.5vw, 0.9rem);
}

/* Animations */
@keyframes headerReveal {
    from {
        opacity: 0;
        transform: translateY(-20px) scale(0.98);
    }
    to {
        opacity: 1;
        transform: translateY(0) scale(1);
    }
}

@keyframes logoPop {
    from {
        opacity: 0;
        transform: scale(0.8);
    }
    to {
        opacity: 1;
        transform: scale(1);
    }
}

@keyframes backgroundPulse {
    0% { opacity: 0.8; }
    100% { opacity: 1; }
}

@keyframes gradientBorder {
    0%, 100% { opacity: 0.3; }
    50% { opacity: 1; }
}

@keyframes textGradient {
    0% { background-position: 0% center; }
    100% { background-position: 200% center; }
}

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

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

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

@keyframes dots {
    0%, 20% { content: '.'; }
    40% { content: '..'; }
    60% { content: '...'; }
    80%, 100% { content: ''; }
}

/* Responsive Design */
@media (max-width: 768px) {
    .container {
        margin-top: calc(var(--spacing) * 6);
    }

    .course-card {
        padding: calc(var(--spacing) * 0.8);
    }

    .lesson {
        padding: calc(var(--spacing) * 0.8);
    }
}

@media (max-width: 480px) {
    :root {
        --spacing: 0.75rem;
    }

    .logo-container {
        padding: 0.5rem 0.75rem;
    }

    h2 {
        margin-bottom: calc(var(--spacing) * 0.5);
    }
}

@media (min-width: 769px) {
    .header-content {
        flex-direction: row;
        justify-content: space-between;
        align-items: center;
    }

    .search-container {
        width: auto;
        max-width: 300px;
        padding: 0 var(--spacing);
    }

    .container {
        margin-top: calc(var(--spacing) * 4);
        padding: calc(var(--spacing) * 2);
    }

    .course-card {
        padding: calc(var(--spacing) * 1.5);
        margin-bottom: calc(var(--spacing) * 2);
    }

    .lesson {
        padding: calc(var(--spacing) * 1.2);
    }
}