:root {
    --primary-color: #2563eb;
    --primary-hover: #1d4ed8;
    --secondary-color: #64748b;
    --success-color: #22c55e;
    --danger-color: #ef4444;
    --warning-color: #f59e0b;
    --background-color: #f8fafc;
    --card-background: #ffffff;
    --text-color: #1e293b;
    --text-muted: #64748b;
    --border-color: #e2e8f0;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
    --radius: 8px;
}

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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: var(--background-color);
    color: var(--text-color);
    line-height: 1.6;
}

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

a:hover {
    text-decoration: underline;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 20px;
}

/* Header */
.header {
    background-color: var(--card-background);
    border-bottom: 1px solid var(--border-color);
    padding: 15px 0;
    position: sticky;
    top: 0;
    z-index: 100;
}

.header .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0 20px;
}

.logo {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--primary-color);
}

.nav {
    display: flex;
    gap: 20px;
    align-items: center;
}

.nav a {
    color: var(--text-color);
    padding: 8px 16px;
    border-radius: var(--radius);
    transition: background-color 0.2s;
}

.nav a:hover {
    background-color: var(--background-color);
    text-decoration: none;
}

.nav a.active {
    background-color: var(--primary-color);
    color: white;
}

.user-info {
    display: flex;
    align-items: center;
    gap: 10px;
}

.user-name {
    font-weight: 500;
}

.user-role {
    font-size: 0.75rem;
    background-color: var(--primary-color);
    color: white;
    padding: 2px 8px;
    border-radius: 12px;
}

/* Buttons */
.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 10px 20px;
    border: none;
    border-radius: var(--radius);
    font-size: 0.95rem;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.2s;
    gap: 8px;
}

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

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

.btn-secondary {
    background-color: var(--secondary-color);
    color: white;
}

.btn-secondary:hover {
    background-color: #475569;
}

.btn-success {
    background-color: var(--success-color);
    color: white;
}

.btn-danger {
    background-color: var(--danger-color);
    color: white;
}

.btn-outline {
    background-color: transparent;
    border: 1px solid var(--border-color);
    color: var(--text-color);
}

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

.btn-sm {
    padding: 6px 12px;
    font-size: 0.85rem;
}

.btn-block {
    width: 100%;
}

/* Cards */
.card {
    background-color: var(--card-background);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    overflow: hidden;
}

.card-header {
    padding: 15px 20px;
    border-bottom: 1px solid var(--border-color);
    background-color: var(--background-color);
}

.card-header h2,
.card-header h3 {
    margin: 0;
}

.card-body {
    padding: 20px;
}

.card-footer {
    padding: 15px 20px;
    border-top: 1px solid var(--border-color);
    background-color: var(--background-color);
}

/* Forms */
.form-group {
    margin-bottom: 20px;
}

.form-label {
    display: block;
    margin-bottom: 6px;
    font-weight: 500;
    color: var(--text-color);
}

.form-control {
    width: 100%;
    padding: 10px 14px;
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    font-size: 1rem;
    transition: border-color 0.2s, box-shadow 0.2s;
}

.form-control:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}

textarea.form-control {
    min-height: 120px;
    resize: vertical;
}

/* Login Page */
.login-container {
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 20px;
}

.login-card {
    width: 100%;
    max-width: 400px;
}

.login-card .card-header {
    text-align: center;
    padding: 30px 20px;
}

.login-card .logo {
    font-size: 2rem;
    margin-bottom: 10px;
}

.login-card .card-body {
    padding: 30px;
}

.login-tabs {
    display: flex;
    margin-bottom: 20px;
}

.login-tab {
    flex: 1;
    padding: 12px;
    text-align: center;
    background-color: var(--background-color);
    border: none;
    cursor: pointer;
    font-weight: 500;
    transition: all 0.2s;
}

.login-tab:first-child {
    border-radius: var(--radius) 0 0 var(--radius);
}

.login-tab:last-child {
    border-radius: 0 var(--radius) var(--radius) 0;
}

.login-tab.active {
    background-color: var(--primary-color);
    color: white;
}

/* Grid */
.grid {
    display: grid;
    gap: 20px;
}

.grid-2 {
    grid-template-columns: repeat(2, 1fr);
}

.grid-3 {
    grid-template-columns: repeat(3, 1fr);
}

.grid-4 {
    grid-template-columns: repeat(4, 1fr);
}

@media (max-width: 992px) {
    .grid-4 {
        grid-template-columns: repeat(2, 1fr);
    }
    .grid-3 {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 576px) {
    .grid-4,
    .grid-3,
    .grid-2 {
        grid-template-columns: 1fr;
    }
}

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

.course-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-lg);
}

.course-thumbnail {
    height: 160px;
    background-color: var(--background-color);
    background-size: cover;
    background-position: center;
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--text-muted);
    font-size: 3rem;
}

.course-info {
    padding: 15px;
}

.course-title {
    font-size: 1.1rem;
    font-weight: 600;
    margin-bottom: 8px;
}

.course-meta {
    font-size: 0.85rem;
    color: var(--text-muted);
}

/* Lesson Sidebar */
.lesson-layout {
    display: grid;
    grid-template-columns: 280px 1fr;
    gap: 20px;
    min-height: calc(100vh - 80px);
}

@media (max-width: 768px) {
    .lesson-layout {
        grid-template-columns: 1fr;
    }
}

.lesson-sidebar {
    background-color: var(--card-background);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    height: fit-content;
    position: sticky;
    top: 90px;
}

.lesson-list {
    list-style: none;
}

.lesson-item {
    border-bottom: 1px solid var(--border-color);
}

.lesson-item:last-child {
    border-bottom: none;
}

.lesson-item a {
    display: block;
    padding: 12px 15px;
    color: var(--text-color);
    transition: background-color 0.2s;
}

.lesson-item a:hover {
    background-color: var(--background-color);
    text-decoration: none;
}

.lesson-item.active a {
    background-color: var(--primary-color);
    color: white;
}

.lesson-number {
    font-size: 0.8rem;
    color: var(--text-muted);
    margin-right: 8px;
}

.lesson-item.active .lesson-number {
    color: rgba(255, 255, 255, 0.7);
}

/* Video Container */
.video-container {
    position: relative;
    padding-bottom: 56.25%;
    height: 0;
    overflow: hidden;
    border-radius: var(--radius);
    background-color: #000;
    margin-bottom: 20px;
}

.video-container iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    border: none;
}

/* Markdown Content */
.markdown-content {
    line-height: 1.8;
}

.markdown-content h1,
.markdown-content h2,
.markdown-content h3 {
    margin-top: 24px;
    margin-bottom: 16px;
}

.markdown-content p {
    margin-bottom: 16px;
}

.markdown-content code {
    background-color: var(--background-color);
    padding: 2px 6px;
    border-radius: 4px;
    font-family: 'Consolas', monospace;
}

.markdown-content pre {
    background-color: #1e293b;
    color: #e2e8f0;
    padding: 16px;
    border-radius: var(--radius);
    overflow-x: auto;
    margin-bottom: 16px;
}

.markdown-content pre code {
    background-color: transparent;
    padding: 0;
    color: inherit;
}

.markdown-content ul,
.markdown-content ol {
    margin-bottom: 16px;
    padding-left: 24px;
}

.markdown-content li {
    margin-bottom: 8px;
}

/* Comments */
.comments-section {
    margin-top: 30px;
}

.comment {
    padding: 15px;
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    margin-bottom: 15px;
    background-color: var(--card-background);
}

.comment-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 10px;
}

.comment-author {
    font-weight: 600;
}

.comment-date {
    font-size: 0.85rem;
    color: var(--text-muted);
}

.comment-body {
    margin-bottom: 10px;
}

.comment-actions {
    display: flex;
    gap: 10px;
}

.comment-replies {
    margin-left: 30px;
    margin-top: 15px;
}

/* Forum */
.topic-list {
    list-style: none;
}

.topic-item {
    padding: 15px;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    justify-content: space-between;
    align-items: center;
    transition: background-color 0.2s;
}

.topic-item:hover {
    background-color: var(--background-color);
}

.topic-item:last-child {
    border-bottom: none;
}

.topic-title {
    font-weight: 600;
    margin-bottom: 4px;
}

.topic-meta {
    font-size: 0.85rem;
    color: var(--text-muted);
}

.topic-stats {
    text-align: right;
}

.post-item {
    padding: 20px;
    border-bottom: 1px solid var(--border-color);
}

.post-item:last-child {
    border-bottom: none;
}

/* Quiz */
.question-card {
    margin-bottom: 30px;
}

.question-stem {
    font-size: 1.1rem;
    font-weight: 500;
    margin-bottom: 15px;
}

.alternatives-list {
    list-style: none;
}

.alternative-item {
    padding: 12px 15px;
    border: 2px solid var(--border-color);
    border-radius: var(--radius);
    margin-bottom: 10px;
    cursor: pointer;
    transition: all 0.2s;
    display: flex;
    align-items: center;
    gap: 12px;
}

.alternative-item:hover {
    border-color: var(--primary-color);
    background-color: rgba(37, 99, 235, 0.05);
}

.alternative-item.selected {
    border-color: var(--primary-color);
    background-color: rgba(37, 99, 235, 0.1);
}

.alternative-item.correct {
    border-color: var(--success-color);
    background-color: rgba(34, 197, 94, 0.1);
}

.alternative-item.incorrect {
    border-color: var(--danger-color);
    background-color: rgba(239, 68, 68, 0.1);
}

.alternative-checkbox {
    width: 20px;
    height: 20px;
    border: 2px solid var(--border-color);
    border-radius: 4px;
    display: flex;
    align-items: center;
    justify-content: center;
    flex-shrink: 0;
}

.alternative-item.selected .alternative-checkbox {
    background-color: var(--primary-color);
    border-color: var(--primary-color);
    color: white;
}

.result-message {
    padding: 15px;
    border-radius: var(--radius);
    margin-top: 15px;
    font-weight: 500;
}

.result-message.success {
    background-color: rgba(34, 197, 94, 0.1);
    color: var(--success-color);
    border: 1px solid var(--success-color);
}

.result-message.error {
    background-color: rgba(239, 68, 68, 0.1);
    color: var(--danger-color);
    border: 1px solid var(--danger-color);
}

/* Alerts */
.alert {
    padding: 15px 20px;
    border-radius: var(--radius);
    margin-bottom: 20px;
}

.alert-success {
    background-color: rgba(34, 197, 94, 0.1);
    color: var(--success-color);
    border: 1px solid var(--success-color);
}

.alert-danger {
    background-color: rgba(239, 68, 68, 0.1);
    color: var(--danger-color);
    border: 1px solid var(--danger-color);
}

.alert-warning {
    background-color: rgba(245, 158, 11, 0.1);
    color: var(--warning-color);
    border: 1px solid var(--warning-color);
}

/* Modal */
.modal-overlay {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: rgba(0, 0, 0, 0.5);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 1000;
    opacity: 0;
    visibility: hidden;
    transition: all 0.3s;
}

.modal-overlay.active {
    opacity: 1;
    visibility: visible;
}

.modal {
    background-color: var(--card-background);
    border-radius: var(--radius);
    width: 100%;
    max-width: 500px;
    max-height: 90vh;
    overflow-y: auto;
    transform: translateY(-20px);
    transition: transform 0.3s;
}

.modal-overlay.active .modal {
    transform: translateY(0);
}

.modal-header {
    padding: 20px;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.modal-header h3 {
    margin: 0;
}

.modal-close {
    background: none;
    border: none;
    font-size: 1.5rem;
    cursor: pointer;
    color: var(--text-muted);
}

.modal-body {
    padding: 20px;
}

.modal-footer {
    padding: 20px;
    border-top: 1px solid var(--border-color);
    display: flex;
    justify-content: flex-end;
    gap: 10px;
}

/* Loading */
.loading {
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 40px;
}

.spinner {
    width: 40px;
    height: 40px;
    border: 4px solid var(--border-color);
    border-top-color: var(--primary-color);
    border-radius: 50%;
    animation: spin 1s linear infinite;
}

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

/* Empty State */
.empty-state {
    text-align: center;
    padding: 60px 20px;
    color: var(--text-muted);
}

.empty-state-icon {
    font-size: 4rem;
    margin-bottom: 20px;
}

.empty-state h3 {
    margin-bottom: 10px;
    color: var(--text-color);
}

/* Badge */
.badge {
    display: inline-block;
    padding: 4px 10px;
    font-size: 0.75rem;
    font-weight: 600;
    border-radius: 12px;
}

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

.badge-success {
    background-color: var(--success-color);
    color: white;
}

.badge-danger {
    background-color: var(--danger-color);
    color: white;
}

/* Page Header */
.page-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 30px;
}

.page-title {
    font-size: 1.75rem;
    font-weight: 700;
}

.breadcrumb {
    display: flex;
    align-items: center;
    gap: 8px;
    font-size: 0.9rem;
    color: var(--text-muted);
    margin-bottom: 15px;
}

.breadcrumb a {
    color: var(--text-muted);
}

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

/* Tab Navigation */
.tabs {
    display: flex;
    border-bottom: 2px solid var(--border-color);
    margin-bottom: 20px;
}

.tab {
    padding: 12px 20px;
    border: none;
    background: none;
    cursor: pointer;
    font-weight: 500;
    color: var(--text-muted);
    border-bottom: 2px solid transparent;
    margin-bottom: -2px;
    transition: all 0.2s;
}

.tab:hover {
    color: var(--primary-color);
}

.tab.active {
    color: var(--primary-color);
    border-bottom-color: var(--primary-color);
}

.tab-content {
    display: none;
}

.tab-content.active {
    display: block;
}

/* Utilities */
.text-center {
    text-align: center;
}

.text-muted {
    color: var(--text-muted);
}

.mt-20 {
    margin-top: 20px;
}

.mb-20 {
    margin-bottom: 20px;
}

.hidden {
    display: none !important;
}

.flex {
    display: flex;
}

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

.gap-10 {
    gap: 10px;
}

.gap-20 {
    gap: 20px;
}

.gap-5 {
    gap: 5px;
}

/* Tables */
.table {
    width: 100%;
    border-collapse: collapse;
}

.table th,
.table td {
    padding: 12px 15px;
    text-align: left;
    border-bottom: 1px solid var(--border-color);
}

.table th {
    background-color: var(--background-color);
    font-weight: 600;
    color: var(--text-muted);
    font-size: 0.85rem;
    text-transform: uppercase;
}

.table tr:hover {
    background-color: var(--background-color);
}

/* Badges */
.badge {
    display: inline-block;
    padding: 4px 10px;
    border-radius: 20px;
    font-size: 0.75rem;
    font-weight: 600;
}

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

.badge-secondary {
    background-color: var(--secondary-color);
    color: white;
}

.badge-success {
    background-color: var(--success-color);
    color: white;
}

.badge-danger {
    background-color: var(--danger-color);
    color: white;
}

.badge-warning {
    background-color: var(--warning-color);
    color: white;
}

/* Button variations */
.btn-success {
    background-color: var(--success-color);
    color: white;
    border: none;
}

.btn-success:hover {
    background-color: #16a34a;
}

.btn-warning {
    background-color: var(--warning-color);
    color: white;
    border: none;
}

.btn-warning:hover {
    background-color: #d97706;
}

.filter-btn.active {
    opacity: 1;
}

.filter-btn:not(.active) {
    opacity: 0.6;
}

/* Notification animations */
@keyframes slideIn {
    from {
        transform: translateX(100%);
        opacity: 0;
    }
    to {
        transform: translateX(0);
        opacity: 1;
    }
}

@keyframes slideOut {
    from {
        transform: translateX(0);
        opacity: 1;
    }
    to {
        transform: translateX(100%);
        opacity: 0;
    }
}