:root {
    /* Dark Theme (Default) */
    --bg-color: #0f172a;
    --card-bg: rgba(30, 41, 59, 0.7);
    --card-border: rgba(51, 65, 85, 0.5);
    --card-hover: rgba(30, 41, 59, 0.95);
    --text-main: #f8fafc;
    --text-muted: #94a3b8;
    --primary: #3b82f6;
    --primary-hover: #2563eb;
    --border: #334155;
    --header-bg: rgba(15, 23, 42, 0.85);
    --input-bg: #1e293b;
    --font-family: 'Inter', sans-serif;
    --glass-shadow: 0 4px 30px rgba(0, 0, 0, 0.1);
    --glass-border: rgba(255, 255, 255, 0.1);
}

[data-theme="light"] {
    --bg-color: #f8fafc;
    --card-bg: rgba(255, 255, 255, 0.8);
    --card-border: rgba(226, 232, 240, 0.8);
    --card-hover: rgba(255, 255, 255, 1);
    --text-main: #0f172a;
    --text-muted: #64748b;
    --primary: #2563eb;
    --primary-hover: #1d4ed8;
    --border: #e2e8f0;
    --header-bg: rgba(248, 250, 252, 0.85);
    --input-bg: #ffffff;
    --glass-shadow: 0 8px 32px rgba(31, 38, 135, 0.05);
    --glass-border: rgba(0, 0, 0, 0.05);
}

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

body {
    background-color: var(--bg-color);
    color: var(--text-main);
    font-family: var(--font-family);
    line-height: 1.6;
    min-height: 100vh;
    transition: background-color 0.3s ease, color 0.3s ease;
}

.container {
    max-width: 1280px;
    margin: 0 auto;
    padding: 0 1.5rem;
}

/* Glassmorphism Header */
header {
    background-color: var(--header-bg);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    border-bottom: 1px solid var(--border);
    padding: 1rem 0;
    position: sticky;
    top: 0;
    z-index: 50;
    box-shadow: var(--glass-shadow);
    transition: all 0.3s ease;
}

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

.logo-area h1 {
    font-size: 1.75rem;
    font-weight: 800;
    background: linear-gradient(135deg, var(--primary), #a78bfa);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    margin: 0;
    letter-spacing: -0.5px;
}

.header-actions {
    display: flex;
    align-items: center;
    gap: 1rem;
}

.icon-btn {
    background: transparent;
    border: none;
    color: var(--text-main);
    cursor: pointer;
    padding: 0.5rem;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: background-color 0.2s;
}

.icon-btn:hover {
    background-color: rgba(128, 128, 128, 0.1);
}

.icon-btn svg {
    width: 24px;
    height: 24px;
}

/* Controls Row */
.controls-row {
    display: flex;
    gap: 1rem;
    align-items: center;
    flex-wrap: wrap;
}

.controls-row.flex-end {
    justify-content: flex-end;
}

.search-container {
    flex: 1;
    max-width: 400px;
    min-width: 280px;
    position: relative;
}

.search-container input {
    background-color: var(--input-bg);
    border: 1px solid var(--border);
    color: var(--text-main);
    padding: 0.75rem 1rem 0.75rem 2.5rem;
    border-radius: 9999px;
    width: 100%;
    font-family: var(--font-family);
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    box-shadow: inset 0 2px 4px 0 rgba(0, 0, 0, 0.05);
}

.search-container::before {
    content: '';
    position: absolute;
    left: 1rem;
    top: 50%;
    transform: translateY(-50%);
    width: 16px;
    height: 16px;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' fill='none' viewBox='0 0 24 24' stroke='%2394a3b8'%3E%3Cpath stroke-linecap='round' stroke-linejoin='round' stroke-width='2' d='M21 21l-6-6m2-5a7 7 0 11-14 0 7 7 0 0114 0z' /%3E%3C/svg%3E");
    background-size: cover;
    pointer-events: none;
}

.search-container input:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 4px rgba(59, 130, 246, 0.2);
}

.custom-select {
    background-color: var(--input-bg);
    border: 1px solid var(--border);
    color: var(--text-main);
    padding: 0.75rem 2rem 0.75rem 1rem;
    border-radius: 0.75rem;
    font-family: var(--font-family);
    cursor: pointer;
    appearance: none;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' fill='none' viewBox='0 0 24 24' stroke='%2394a3b8'%3E%3Cpath stroke-linecap='round' stroke-linejoin='round' stroke-width='2' d='M19 9l-7 7-7-7' /%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 0.75rem center;
    background-size: 16px;
    transition: all 0.2s;
}

.custom-select:focus {
    outline: none;
    border-color: var(--primary);
}

main {
    padding: 2.5rem 0;
    animation: fadeIn 0.4s ease-out;
}

.section-header {
    display: flex;
    flex-wrap: wrap;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 2rem;
    gap: 1rem;
}

.section-header h2 {
    font-size: 1.875rem;
    font-weight: 700;
}

/* Loading & Empty States */
.loading, .error, .empty-state {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: 5rem 1rem;
    text-align: center;
    color: var(--text-muted);
}

.spinner {
    width: 48px;
    height: 48px;
    border: 3px solid rgba(128, 128, 128, 0.2);
    border-left-color: var(--primary);
    border-radius: 50%;
    animation: spin 1s cubic-bezier(0.4, 0, 0.2, 1) infinite;
    margin-bottom: 1.5rem;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

/* Skeleton Loading (Shimmer) */
.skeleton {
    background: linear-gradient(90deg, var(--card-bg) 25%, var(--border) 50%, var(--card-bg) 75%);
    background-size: 200% 100%;
    animation: shimmer 1.5s infinite linear;
    border-radius: 0.5rem;
}

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

.hidden { display: none !important; }

/* Grids */
.grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 2rem;
}

.topics-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 1.5rem;
}

.videos-grid-modern {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 1.5rem;
}

/* Cards (Glassmorphism & Modern) */
.card, .topic-card, .video-card {
    background: var(--card-bg);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border: 1px solid var(--card-border);
    border-radius: 1.25rem;
    overflow: hidden;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    text-decoration: none;
    color: inherit;
    display: flex;
    flex-direction: column;
    box-shadow: var(--glass-shadow);
    cursor: pointer;
    position: relative;
}

.card:hover, .topic-card:hover, .video-card:hover {
    transform: translateY(-8px);
    box-shadow: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
    border-color: var(--primary);
    background: var(--card-hover);
}

.card-img-container, .video-thumb-container {
    width: 100%;
    aspect-ratio: 16 / 9;
    overflow: hidden;
    background-color: var(--input-bg);
    position: relative;
}

.card-img, .video-thumb-container img {
    width: 100%;
    height: 100%;
    object-fit: cover;
    transition: transform 0.7s cubic-bezier(0.4, 0, 0.2, 1);
}

.card:hover .card-img, .video-card:hover .video-thumb-container img {
    transform: scale(1.08);
}

.play-overlay {
    position: absolute;
    inset: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    background: rgba(0, 0, 0, 0.4);
    backdrop-filter: blur(2px);
    opacity: 0;
    transition: all 0.3s ease;
}

.video-card:hover .play-overlay {
    opacity: 1;
}

.play-overlay svg {
    width: 64px;
    height: 64px;
    color: white;
    filter: drop-shadow(0 4px 6px rgba(0,0,0,0.5));
    transform: scale(0.8);
    transition: transform 0.3s cubic-bezier(0.34, 1.56, 0.64, 1);
}

.video-card:hover .play-overlay svg {
    transform: scale(1);
}

.card-content, .topic-content-modern, .video-info {
    padding: 1.5rem;
    flex-grow: 1;
    display: flex;
    flex-direction: column;
}

.card-title, .topic-title, .video-title {
    font-size: 1.125rem;
    font-weight: 600;
    margin-bottom: 0.75rem;
    line-height: 1.4;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;
    overflow: hidden;
    color: var(--text-main);
}

.topic-card {
    padding: 1.5rem;
    flex-direction: row;
    align-items: center;
    gap: 1rem;
}

.topic-icon-large {
    width: 56px;
    height: 56px;
    border-radius: 1rem;
    background: linear-gradient(135deg, rgba(59,130,246,0.1), rgba(167,139,250,0.1));
    color: var(--primary);
    display: flex;
    align-items: center;
    justify-content: center;
    flex-shrink: 0;
}

.topic-icon-large svg {
    width: 28px;
    height: 28px;
}

.topic-info {
    flex-grow: 1;
}

.topic-info h3 {
    font-size: 1.125rem;
    font-weight: 600;
    margin-bottom: 0.25rem;
}

.badge {
    background: rgba(59, 130, 246, 0.15);
    color: var(--primary);
    padding: 0.25rem 0.75rem;
    border-radius: 9999px;
    font-size: 0.8rem;
    font-weight: 600;
    display: inline-block;
}

.card-footer {
    margin-top: auto;
    display: flex;
    justify-content: space-between;
    align-items: center;
    border-top: 1px solid var(--border);
    padding-top: 1.25rem;
}

.card-date, .video-meta {
    font-size: 0.875rem;
    color: var(--text-muted);
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-weight: 500;
}

.btn-link {
    background: linear-gradient(135deg, var(--primary), #60a5fa);
    color: white;
    padding: 0.5rem 1.25rem;
    border-radius: 9999px;
    font-size: 0.875rem;
    font-weight: 600;
    border: none;
    box-shadow: 0 4px 14px 0 rgba(59, 130, 246, 0.39);
    transition: all 0.2s ease;
}

.card:hover .btn-link {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(59, 130, 246, 0.5);
}

/* Pagination Controls */
.pagination-controls {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 1rem;
    margin-top: 3rem;
    padding-top: 2rem;
    border-top: 1px solid var(--border);
}

.btn-pagination {
    background-color: var(--card-bg);
    border: 1px solid var(--border);
    color: var(--text-main);
    padding: 0.5rem 1rem;
    border-radius: 0.5rem;
    cursor: pointer;
    font-weight: 500;
    transition: all 0.2s;
}

.btn-pagination:hover:not(:disabled) {
    border-color: var(--primary);
    color: var(--primary);
}

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

.page-numbers {
    display: flex;
    gap: 0.5rem;
}

.page-num {
    width: 36px;
    height: 36px;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 0.5rem;
    cursor: pointer;
    font-weight: 500;
    transition: all 0.2s;
}

.page-num:hover:not(.active) {
    background-color: rgba(128,128,128,0.1);
}

.page-num.active {
    background-color: var(--primary);
    color: white;
    box-shadow: 0 4px 14px rgba(59, 130, 246, 0.4);
}

/* Details Header (Batch/Topic) */
.details-header {
    margin-bottom: 2rem;
    padding-bottom: 1.5rem;
    border-bottom: 1px solid var(--border);
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 1.5rem;
}

.btn-back {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    background: var(--card-bg);
    border: 1px solid var(--border);
    color: var(--text-main);
    padding: 0.75rem 1.25rem;
    border-radius: 9999px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s ease;
}

.btn-back:hover {
    border-color: var(--primary);
    color: var(--primary);
    transform: translateX(-4px);
}

.details-title-wrapper {
    flex-grow: 1;
}

.details-title-wrapper h2 {
    font-size: 2rem;
    font-weight: 800;
    margin-bottom: 0.25rem;
}

/* Floating Scroll to Top */
.scroll-to-top {
    position: fixed;
    bottom: 2rem;
    right: 2rem;
    width: 50px;
    height: 50px;
    background-color: var(--primary);
    color: white;
    border: none;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    box-shadow: 0 10px 25px rgba(59, 130, 246, 0.5);
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    z-index: 100;
    opacity: 0;
    transform: translateY(20px);
    pointer-events: none;
}

.scroll-to-top.visible {
    opacity: 1;
    transform: translateY(0);
    pointer-events: auto;
}

.scroll-to-top:hover {
    background-color: var(--primary-hover);
    transform: translateY(-5px);
}

.scroll-to-top svg {
    width: 24px;
    height: 24px;
}

/* Toast Container */
.toast-container {
    position: fixed;
    bottom: 2rem;
    left: 50%;
    transform: translateX(-50%);
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
    z-index: 1000;
    pointer-events: none;
}

.toast {
    background: var(--card-bg);
    backdrop-filter: blur(10px);
    border: 1px solid var(--card-border);
    color: var(--text-main);
    padding: 0.75rem 1.5rem;
    border-radius: 9999px;
    font-weight: 500;
    box-shadow: 0 10px 25px rgba(0,0,0,0.2);
    animation: slideUp 0.3s ease-out;
    pointer-events: auto;
}

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

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

/* Animations */
.animate-fade-in { animation: fadeIn 0.4s ease-out forwards; }

@media (max-width: 768px) {
    .controls-row {
        flex-direction: column;
        align-items: stretch;
    }
    
    .search-container {
        max-width: 100%;
    }
    
    .details-header {
        flex-direction: column;
        align-items: flex-start;
    }
    
    .scroll-to-top {
        bottom: 1rem;
        right: 1rem;
    }
}

/* YouTube like Player Modifications */
.plyr--video .plyr__control--overlaid {
    background: rgba(255, 0, 0, 0.8) !important;
}
.plyr--video .plyr__control.plyr__tab-focus,
.plyr--video .plyr__control:hover,
.plyr--video .plyr__control[aria-expanded=true] {
    background: #ff0000 !important;
}
.plyr--full-ui input[type=range] {
    color: #ff0000 !important;
}
.plyr__video-wrapper {
    touch-action: manipulation; /* Makes mobile double tap registration smoother */
}