:root {
    --primary-color: #4f46e5;
    --primary-color-rgb: 79, 70, 229;
    --primary-color-light: #6366f1;
    --primary-color-dark: #4338ca;
    --secondary-color: #8b5cf6;
    --secondary-color-light: #a78bfa;
    --text-primary: #1f2937;
    --text-secondary: #4b5563;
    --bg-primary: #ffffff;
    --bg-secondary: #f9fafb;
    --bg-card: #ffffff;
    --border-color: #e5e7eb;
    --shadow-color: rgba(0, 0, 0, 0.08);
    --shadow-color-hover: rgba(0, 0, 0, 0.12);
    --transition-speed: 0.3s;
}

.dark {
    --primary-color: #6366f1;
    --primary-color-rgb: 99, 102, 241;
    --primary-color-light: #818cf8;
    --primary-color-dark: #4f46e5;
    --secondary-color: #a78bfa;
    --secondary-color-light: #c4b5fd;
    --text-primary: #f9fafb;
    --text-secondary: #d1d5db;
    --bg-primary: #111827;
    --bg-secondary: #1f2937;
    --bg-card: #1f2937;
    --border-color: #374151;
    --shadow-color: rgba(0, 0, 0, 0.3);
    --shadow-color-hover: rgba(0, 0, 0, 0.4);
}

body {
    font-family: 'Inter', system-ui, -apple-system, sans-serif;
    background-color: var(--bg-primary);
    color: var(--text-primary);
    transition: background-color var(--transition-speed), color var(--transition-speed);
    line-height: 1.5;
    letter-spacing: 0.01em;
}

.container {
    max-width: 1280px;
    margin: 0 auto;
    padding: 0 1rem;
}

.navbar {
    background-color: var(--bg-primary);
    border-bottom: 1px solid var(--border-color);
    position: sticky;
    top: 0;
    z-index: 100;
    transition: background-color var(--transition-speed), border-color var(--transition-speed);
}

.card {
    background-color: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: 0.75rem;
    overflow: hidden;
    transition: transform 0.3s ease, box-shadow 0.3s ease, border-color var(--transition-speed), background-color var(--transition-speed);
    height: 100%;
    display: flex;
    flex-direction: column;
    box-shadow: 0 4px 6px var(--shadow-color);
}

.card:hover {
    transform: translateY(-6px);
    box-shadow: 0 12px 20px -5px var(--shadow-color-hover);
    border-color: var(--primary-color-light);
}

.btn {
    transition: all 0.3s ease;
    position: relative;
    overflow: hidden;
    background: linear-gradient(135deg, var(--primary-color), var(--primary-color-dark));
    border: none;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
}

.btn:hover {
    transform: scale(1.05);
    box-shadow: 0 6px 10px rgba(0, 0, 0, 0.15);
    background: linear-gradient(135deg, var(--primary-color-light), var(--primary-color));
}

.btn:active {
    transform: scale(0.98);
}

.subject-badge {
    background: linear-gradient(135deg, var(--secondary-color), var(--secondary-color-light));
    color: white;
    font-size: 0.75rem;
    padding: 0.35rem 0.7rem;
    border-radius: 9999px;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
    transition: all 0.3s ease;
    font-weight: 500;
    letter-spacing: 0.02em;
}

.subject-badge:hover {
    transform: translateY(-1px);
    box-shadow: 0 3px 6px rgba(0, 0, 0, 0.15);
}

.theme-toggle {
    cursor: pointer;
    padding: 0.5rem;
    border-radius: 9999px;
    transition: all 0.3s ease;
    position: relative;
    width: 2.5rem;
    height: 2.5rem;
    display: flex;
    align-items: center;
    justify-content: center;
}

.theme-toggle:hover {
    background-color: var(--bg-secondary);
    transform: rotate(15deg);
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
}

.section-title {
    color: var(--text-primary);
    font-weight: 700;
    margin-bottom: 1.5rem;
    position: relative;
    display: inline-block;
    letter-spacing: 0.02em;
}

.section-title::after {
    content: '';
    position: absolute;
    bottom: -0.5rem;
    left: 0;
    width: 3rem;
    height: 0.25rem;
    background: linear-gradient(90deg, var(--primary-color), var(--secondary-color));
    border-radius: 0.125rem;
    transition: width 0.3s ease;
}

.section-title:hover::after {
    width: 100%;
}

.select-container {
    position: relative;
    width: 40%;
}

.education-level-select {
    width: 100%;
    min-width: 120px;
    padding-right: 2rem;
}

select {
    appearance: none;
    background-color: var(--bg-card);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
    transition: border-color var(--transition-speed), background-color var(--transition-speed);
}

.select-container::after {
    content: '\f078';
    font-family: 'Font Awesome 5 Free';
    font-weight: 900;
    position: absolute;
    right: 1rem;
    top: 50%;
    transform: translateY(-50%);
    color: var(--text-secondary);
    pointer-events: none;
}

.card-img-container {
    position: relative;
    overflow: hidden;
    height: 120px;
    border-bottom: 1px solid var(--border-color);
    background-color: var(--bg-secondary);
}

.card .p-4 {
    display: flex;
    flex-direction: column;
    flex: 1;
    height: 100%;
}

.video-item {
    height: 220px; /* 固定卡片高度 */
    cursor: pointer;
    position: relative;
}

.video-item .description-text {
    overflow: hidden;
    text-overflow: ellipsis;
    display: -webkit-box;
    -webkit-line-clamp: 2;
    -webkit-box-orient: vertical;
    line-height: 1.4;
    margin-top: auto;
    color: var(--text-secondary);
    transition: color 0.3s ease;
}

.video-item:hover .description-text {
    color: var(--text-primary);
}

.video-item .author {
    font-weight: 600;
    color: var(--primary-color);
    transition: color 0.3s ease;
}

.video-item:hover .author {
    color: var(--primary-color-light);
}

.card-img-top {
    width: 100%;
    height: 100%;
    object-fit: cover;
    transition: transform 0.5s ease;
    filter: brightness(0.95);
}

.card:hover .card-img-top {
    transform: scale(1.08);
    filter: brightness(1.05);
}

.placeholder-img {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    display: flex;
    align-items: center;
    justify-content: center;
    background-color: var(--bg-secondary);
}

.fallback-img {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    display: none;
    align-items: center;
    justify-content: center;
    flex-direction: column;
    background-color: var(--bg-secondary);
    padding: 1rem;
    text-align: center;
}

.pagination {
    display: flex;
    justify-content: center;
    margin-top: 2rem;
    margin-bottom: 2rem;
}

.pagination-item {
    margin: 0 0.25rem;
    min-width: 2.5rem;
    height: 2.5rem;
    display: flex;
    align-items: center;
    justify-content: center;
    border-radius: 0.5rem;
    background-color: var(--bg-card);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
    transition: all 0.3s ease;
    cursor: pointer;
    padding: 0 0.5rem;
    font-size: 0.875rem;
    user-select: none;
    position: relative;
    overflow: hidden;
    font-weight: 500;
    box-shadow: 0 2px 4px var(--shadow-color);
}

.pagination-item::before {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 0;
    height: 0;
    background-color: rgba(255, 255, 255, 0.2);
    border-radius: 50%;
    transform: translate(-50%, -50%);
    transition: width 0.4s, height 0.4s;
    z-index: 0;
}

.pagination-item:hover::before {
    width: 150%;
    height: 150%;
}

.pagination-item > * {
    position: relative;
    z-index: 1;
}

.pagination-item:hover {
    background-color: var(--primary-color);
    color: white;
    transform: translateY(-3px);
    box-shadow: 0 5px 10px rgba(0, 0, 0, 0.15);
}

/* 搜索按钮样式 */
#search-button {
    cursor: pointer;
    transition: all 0.3s ease;
}

#search-button:hover {
    transform: translateY(-50%) scale(1.1);
    color: var(--primary-color);
}

#search-button:active {
    transform: translateY(-50%) scale(0.95);
    opacity: 0.8;
}

.pagination-item.active {
    background: linear-gradient(135deg, var(--primary-color), var(--primary-color-dark));
    color: white;
    font-weight: 600;
    box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
    border-color: var(--primary-color);
} 

.pagination-item.disabled {
    opacity: 0.5;
    cursor: not-allowed;
    pointer-events: none;
}

.pagination-item.disabled:hover {
    background-color: var(--bg-card);
    color: var(--text-primary);
    transform: none;
    box-shadow: none;
}

.pagination-item.ellipsis {
    background-color: transparent;
    border: none;
    font-weight: bold;
    cursor: default;
}

.pagination-item.ellipsis:hover {
    background-color: transparent;
    color: var(--text-primary);
    transform: none;
    box-shadow: none;
}

.pagination-item.first-page,
.pagination-item.last-page {
    font-size: 0.75rem;
}

.pagination-info {
    margin-top: 1rem;
    text-align: center;
    font-size: 0.875rem;
    color: var(--text-secondary);
}

/* 动画效果 */
@keyframes fadeIn {
    from { opacity: 0; transform: translateY(15px); }
    to { opacity: 1; transform: translateY(0); }
}

.fade-in {
    animation: fadeIn 0.6s cubic-bezier(0.215, 0.61, 0.355, 1) forwards;
}

.video-item {
    opacity: 0;
    animation: fadeIn 0.6s cubic-bezier(0.215, 0.61, 0.355, 1) forwards;
}

.video-item:nth-child(1) { animation-delay: 0.05s; }
.video-item:nth-child(2) { animation-delay: 0.1s; }
.video-item:nth-child(3) { animation-delay: 0.15s; }
.video-item:nth-child(4) { animation-delay: 0.2s; }
.video-item:nth-child(5) { animation-delay: 0.25s; }
.video-item:nth-child(6) { animation-delay: 0.3s; }
.video-item:nth-child(7) { animation-delay: 0.35s; }
.video-item:nth-child(8) { animation-delay: 0.4s; }
.video-item:nth-child(9) { animation-delay: 0.45s; }
.video-item:nth-child(10) { animation-delay: 0.5s; }
.video-item:nth-child(11) { animation-delay: 0.55s; }
.video-item:nth-child(12) { animation-delay: 0.6s; }

/* 加载动画 */
.spinner {
    width: 2.5rem;
    height: 2.5rem;
    border: 3px solid rgba(var(--primary-color-rgb), 0.2);
    border-radius: 50%;
    border-top-color: var(--primary-color);
    border-left-color: var(--primary-color-light);
    animation: spin 1.2s cubic-bezier(0.5, 0.1, 0.5, 0.9) infinite;
    box-shadow: 0 0 10px rgba(var(--primary-color-rgb), 0.1);
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

/* 滚动条样式 */
::-webkit-scrollbar {
    width: 10px;
    height: 10px;
}

::-webkit-scrollbar-track {
    background: var(--bg-secondary);
    border-radius: 5px;
}

::-webkit-scrollbar-thumb {
    background: linear-gradient(to bottom, var(--text-secondary), rgba(var(--primary-color-rgb), 0.5));
    border-radius: 5px;
    border: 2px solid var(--bg-secondary);
}

::-webkit-scrollbar-thumb:hover {
    background: linear-gradient(to bottom, var(--primary-color-light), var(--primary-color));
}

/* 响应式调整 */
@media (max-width: 640px) {
    .section-title {
        font-size: 1.5rem;
    }
    
    .card-img-container {
        height: 140px;
    }
    
    .card {
        border-radius: 0.5rem;
    }
    
    .video-item {
        height: 240px;
    }
    
    .pagination-item {
        min-width: 2.2rem;
        height: 2.2rem;
        font-size: 0.8rem;
    }
}

@media (min-width: 1280px) {
    .card-img-container {
        height: 160px;
    }
    
    .container {
        padding: 0 2rem;
    }
    
    .video-item {
        height: 240px;
    }
}