/* —— CSS-переменные для современной палитры и отступов —— */
:root {
    --color-bg: #f8fafc;
    --color-card: #ffffff;
    --color-primary: #3b82f6;
    --color-primary-hover: #2563eb;
    --color-youtube: #ef4444;
    --color-youtube-hover: #dc2626;
    --color-onedrive: #0364B8;
    --color-onedrive-hover: #025aa3;
    --color-text: #1f2937;
    --color-text-secondary: #4b5563;
    --shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-hover: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    --radius: 12px;
    --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    --spacing: 1rem;
}

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

html, body {
    height: 100%;
}

body {
    font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
    background: var(--color-bg);
    color: var(--color-text);
    line-height: 1.6;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 var(--spacing);
    width: 100%;
}

/* Header & Footer */
.site-header {
    background: linear-gradient(135deg, #1e40af, #1e3a8a);
    color: #fff;
    text-align: center;
    padding: calc(var(--spacing) * 3) 0;
    margin-bottom: calc(var(--spacing) * 2);
    box-shadow: var(--shadow);
}

.site-header h1 {
    font-size: 2.5rem;
    font-weight: 700;
    margin-bottom: var(--spacing);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
}

.back-link {
    color: #fff;
    text-decoration: none;
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.5rem 1rem;
    border-radius: var(--radius);
    background: rgba(255, 255, 255, 0.1);
    transition: var(--transition);
    margin-bottom: var(--spacing);
}

.back-link:hover {
    background: rgba(255, 255, 255, 0.2);
    transform: translateX(-5px);
}

main {
    flex: 1;
    padding: calc(var(--spacing) * 2) 0;
}

.site-footer {
    background: #111827;
    color: #fff;
    text-align: center;
    padding: calc(var(--spacing) * 2) 0;
    margin-top: auto;
}

.site-footer p {
    font-size: 0.9rem;
}

/* Сортировка */
.sort-container {
    margin-bottom: calc(var(--spacing) * 2);
    text-align: right;
    font-size: 0.9rem;
    display: flex;
    align-items: center;
    justify-content: flex-end;
    gap: 0.5rem;
}

.sort-container select {
    padding: 0.5rem 1rem;
    border: 1px solid #e5e7eb;
    border-radius: var(--radius);
    background: var(--color-card);
    cursor: pointer;
    transition: var(--transition);
}

.sort-container select:hover {
    border-color: var(--color-primary);
}

/* Сетка уроков */
#lessons-container {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(350px, 1fr));
    gap: calc(var(--spacing) * 1.5);
    margin-bottom: calc(var(--spacing) * 2);
}

/* Карточка урока */
.lesson-card {
    background: var(--color-card);
    border-radius: var(--radius);
    padding: calc(var(--spacing) * 1.5);
    box-shadow: var(--shadow);
    transition: var(--transition);
    position: relative;
    overflow: hidden;
}

.lesson-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 4px;
    background: var(--color-primary);
    transform: scaleX(0);
    transition: var(--transition);
    transform-origin: left;
}

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

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

.lesson-card h2 {
    margin-bottom: var(--spacing);
    font-size: 1.5rem;
    color: var(--color-text);
}

.lesson-card .date {
    color: var(--color-text-secondary);
    font-size: 0.9rem;
    margin-bottom: var(--spacing);
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.lesson-card .description {
    margin-bottom: var(--spacing);
    color: var(--color-text-secondary);
}

/* Ссылки */
.lesson-card .links {
    display: flex;
    flex-wrap: wrap;
    gap: var(--spacing);
}

.lesson-card .links a {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.75rem 1.25rem;
    border-radius: var(--radius);
    transition: var(--transition);
    background: var(--color-primary);
    color: #fff;
    font-size: 0.9rem;
    text-decoration: none;
    font-weight: 500;
}

.lesson-card .links a:hover {
    background: var(--color-primary-hover);
    transform: translateY(-2px);
}

/* Иконки */
.links a .fa-file-pdf {
    color: #fff;
}

.links a .fa-file-video {
    color: #fff;
}

.links a .fa-play {
    color: #fff;
}

/* YouTube-миниатюры */
.lesson-card .thumbnail {
    max-width: 100%;
    border-radius: var(--radius);
    transition: var(--transition);
}

.youtube-link {
    background: var(--color-youtube);
    position: relative;
    overflow: hidden;
}

.youtube-link:hover {
    background: var(--color-youtube-hover);
}

.youtube-link .fa-play {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    font-size: 2rem;
    opacity: 0.9;
    transition: var(--transition);
}

.youtube-link:hover .fa-play {
    transform: translate(-50%, -50%) scale(1.1);
    opacity: 1;
}

/* Модальное окно */
.lightbox {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.9);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 1000;
    opacity: 0;
    transition: opacity 0.3s ease;
}

.lightbox:not(.hidden) {
    opacity: 1;
}

.lightbox.hidden {
    display: none;
}

.lightbox-content {
    position: relative;
    max-width: 90%;
    max-height: 90%;
    background: #000;
    border-radius: var(--radius);
    overflow: hidden;
}

.lightbox-close {
    position: absolute;
    top: -2.5rem;
    right: -2.5rem;
    background: none;
    border: none;
    color: #fff;
    cursor: pointer;
    font-size: 1.5rem;
    transition: var(--transition);
    z-index: 1001;
}

.lightbox-close:hover {
    transform: rotate(90deg);
}

#lightbox-iframe {
    width: 100%;
    height: 100%;
    min-height: 400px;
    border: none;
}

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

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

/* Адаптивность */
@media (max-width: 768px) {
    .container {
        padding: 0 calc(var(--spacing) * 1.5);
    }

    .site-header h1 {
        font-size: 2rem;
    }

    #lessons-container {
        grid-template-columns: 1fr;
    }

    .lightbox-content {
        max-width: 95%;
        max-height: 95%;
    }

    .lightbox-close {
        top: -2rem;
        right: 0;
    }
}

/* Material page specific styles */
#lesson-description {
    background: var(--color-card);
    padding: calc(var(--spacing) * 2);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    margin-bottom: calc(var(--spacing) * 2);
    font-size: 1.1rem;
    line-height: 1.8;
}

#links-container {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: calc(var(--spacing) * 1.5);
    margin-bottom: calc(var(--spacing) * 2);
}

.file-link {
    display: flex;
    align-items: center;
    gap: 1rem;
    padding: 1.5rem;
    background: var(--color-card);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    transition: var(--transition);
    text-decoration: none;
    color: var(--color-text);
    cursor: pointer;
}

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

.file-link i {
    font-size: 2rem;
}

.file-link.onedrive-link i {
    color: var(--color-onedrive);
}

.file-link.youtube-link i {
    color: var(--color-youtube);
}

.file-link .file-info {
    flex: 1;
}

.file-link .file-title {
    font-weight: 500;
    margin-bottom: 0.5rem;
}

.file-link .file-type {
    font-size: 0.9rem;
    color: var(--color-text-secondary);
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.file-link .file-type i {
    font-size: 1rem;
}

.file-link .preview-icon {
    color: var(--color-text-secondary);
    transition: var(--transition);
}

.file-link:hover .preview-icon {
    color: var(--color-primary);
    transform: scale(1.1);
}

/* PDF Preview */
.pdf-preview {
    position: relative;
    width: 100%;
    height: 500px;
    border-radius: var(--radius);
    overflow: hidden;
    margin-top: var(--spacing);
    box-shadow: var(--shadow);
}

.pdf-preview iframe {
    width: 100%;
    height: 100%;
    border: none;
}

/* PDF Preview Popup */
.pdf-popup {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.8);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 1000;
    opacity: 0;
    visibility: hidden;
    transition: opacity 0.3s ease, visibility 0.3s ease;
}

.pdf-popup.active {
    opacity: 1;
    visibility: visible;
}

.pdf-popup-content {
    position: relative;
    width: 90%;
    max-width: 1200px;
    height: 90vh;
    background: var(--color-card);
    border-radius: var(--radius);
    overflow: hidden;
    display: flex;
    flex-direction: column;
}

.pdf-popup-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 1rem;
    background: #f8fafc;
    border-bottom: 1px solid #e5e7eb;
}

.pdf-popup-title {
    font-weight: 500;
    color: var(--color-text);
}

.pdf-popup-actions {
    display: flex;
    gap: 0.5rem;
}

.pdf-popup-button {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.5rem 1rem;
    border-radius: var(--radius);
    border: none;
    cursor: pointer;
    font-size: 0.9rem;
    transition: var(--transition);
}

.pdf-popup-button.primary {
    background: var(--color-primary);
    color: white;
}

.pdf-popup-button.primary:hover {
    background: var(--color-primary-hover);
}

.pdf-popup-button.secondary {
    background: #e5e7eb;
    color: var(--color-text);
}

.pdf-popup-button.secondary:hover {
    background: #d1d5db;
}

.pdf-popup-close {
    position: absolute;
    top: 1rem;
    right: 1rem;
    background: none;
    border: none;
    color: var(--color-text-secondary);
    cursor: pointer;
    font-size: 1.5rem;
    transition: var(--transition);
    z-index: 1001;
}

.pdf-popup-close:hover {
    color: var(--color-text);
    transform: rotate(90deg);
}

.pdf-popup-iframe {
    flex: 1;
    width: 100%;
    border: none;
    background: white;
}

/* YouTube Link Specific */
.youtube-link {
    position: relative;
    overflow: hidden;
}

.youtube-link .thumbnail {
    width: 100%;
    height: 200px;
    object-fit: cover;
    border-radius: var(--radius);
    transition: var(--transition);
}

.youtube-link:hover .thumbnail {
    transform: scale(1.05);
}

.youtube-link .fa-play {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    font-size: 3rem;
    color: white;
    text-shadow: 0 2px 4px rgba(0, 0, 0, 0.3);
    transition: var(--transition);
}

.youtube-link:hover .fa-play {
    transform: translate(-50%, -50%) scale(1.1);
}

/* OneDrive Link Specific */
.onedrive-link {
    background: linear-gradient(to right, var(--color-card), #f8fafc);
}

.onedrive-link:hover {
    background: linear-gradient(to right, var(--color-card), #f0f4f8);
}

.onedrive-link .file-type {
    color: var(--color-onedrive);
}