* {
    box-sizing: border-box;
}

:root {
    --primary-color: #005f73;
    --secondary-color: #0a9396;
    --background-color: #f0f4f8;
    --card-background: #ffffff;
    --text-color: #333;
    --heading-color: #003440;
    --muted-color: #6c757d;
    --border-color: #dee2e6;
    --shadow-color: rgba(0, 0, 0, 0.08);
    --accent-color-info: #0077b6;
    --accent-color-cta: #2a9d8f;
}

body {
    font-family: "Noto Sans TC", "Microsoft YaHei", sans-serif;
    background-color: var(--background-color);
    margin: 0;
    padding: 24px;
    color: var(--text-color);
    line-height: 1.7;
}

.page-header {
    position: relative;
    text-align: center;
    margin-bottom: 40px;
}

.page-header h1 {
    font-size: 2.25rem;
    color: var(--heading-color);
    font-weight: 700;
    margin: 0;
    line-height: 1.4;
}

.page-header .last-updated,
.page-header p {
    display: block;
    font-size: 1rem;
    color: var(--muted-color);
    font-weight: 400;
    margin: 8px 0 0;
    letter-spacing: 1px;
}

.catalog-admin-link {
    position: absolute;
    top: 0;
    right: 0;
    color: var(--muted-color);
    font-size: 13px;
    text-decoration: none;
}

.catalog-admin-link:hover {
    color: var(--primary-color);
    text-decoration: underline;
}

.course-grid,
.catalog-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(340px, 1fr));
    gap: 24px;
    max-width: 1200px;
    margin: 0 auto;
}

.course-card {
    background: var(--card-background);
    border-radius: 12px;
    box-shadow: 0 4px 12px var(--shadow-color);
    border: 1px solid var(--border-color);
    display: flex;
    flex-direction: column;
    transition: transform 0.2s ease-in-out, box-shadow 0.2s ease-in-out;
}

.course-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 8px 20px var(--shadow-color);
}

.card-header {
    padding: 16px 20px;
    border-bottom: 1px solid var(--border-color);
    display: flex;
    align-items: center;
    gap: 12px;
}

.lesson-badge {
    background-color: var(--primary-color);
    color: #fff;
    min-width: 32px;
    height: 32px;
    border-radius: 50%;
    display: flex;
    justify-content: center;
    align-items: center;
    font-weight: 700;
    font-size: 1rem;
    flex-shrink: 0;
}

.card-header h3 {
    margin: 0;
    color: var(--heading-color);
    font-size: 1.1rem;
    font-weight: 700;
}

.card-body {
    padding: 8px 20px;
    flex-grow: 1;
}

details {
    margin: 12px 0;
    border-radius: 8px;
    border: 1px solid #e9ecef;
    overflow: hidden;
}

details summary {
    padding: 10px 16px 10px 36px;
    font-weight: 500;
    color: var(--primary-color);
    background-color: #f8f9fa;
    cursor: pointer;
    list-style: none;
    position: relative;
}

details summary::-webkit-details-marker {
    display: none;
}

details summary::before {
    content: "\25B6";
    position: absolute;
    left: 14px;
    top: 50%;
    transform: translateY(-50%) rotate(0deg);
    transition: transform 0.2s;
    font-size: 0.8em;
}

details[open] > summary::before {
    transform: translateY(-50%) rotate(90deg);
}

details ul {
    padding: 10px 16px 10px 36px;
    margin: 0;
    font-size: 0.9rem;
}

details li {
    margin-bottom: 6px;
}

.card-footer {
    padding: 12px 20px;
    background-color: #f8f9fa;
    color: var(--muted-color);
    font-size: 0.85rem;
    text-align: right;
    border-top: 1px solid var(--border-color);
    border-bottom-left-radius: 12px;
    border-bottom-right-radius: 12px;
}

.cta-card {
    background: linear-gradient(135deg, #e0f2f1, #e8f5e9);
    border-color: var(--accent-color-cta);
}

.cta-card h3 {
    color: #1b4332;
    font-size: 1.25rem;
    margin-bottom: 12px;
}

.cta-card a,
.qr-card a:not(.qq-group-link) {
    color: var(--accent-color-cta);
    font-weight: 500;
    text-decoration: none;
    transition: color 0.2s;
}

.cta-card a:hover,
.qr-card a:not(.qq-group-link):hover {
    color: #1b4332;
    text-decoration: underline;
}

.cta-card ul {
    list-style: none;
    padding-left: 0;
}

.cta-card li {
    margin-bottom: 8px;
}

.qr-card .card-body {
    text-align: center;
    padding: 24px;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
}

.qr-card img {
    max-width: 200px;
    width: 100%;
    height: auto;
    border-radius: 8px;
    margin-bottom: 16px;
}

.qr-card p {
    margin-top: 0;
    margin-bottom: 16px;
    font-size: 0.95rem;
    color: var(--heading-color);
}

.qq-group-link {
    display: inline-block;
    background-color: #1e90ff;
    color: #fff !important;
    padding: 10px 20px;
    border-radius: 8px;
    text-decoration: none;
    font-weight: 500;
    transition: background-color 0.2s, transform 0.2s;
}

.qq-group-link:hover {
    background-color: #0073e6;
    color: #fff !important;
    text-decoration: none;
    transform: scale(1.05);
}

.empty-state,
.error-state {
    grid-column: 1 / -1;
    padding: 28px;
    border: 1px solid var(--border-color);
    border-radius: 12px;
    background: #fff;
    color: var(--muted-color);
    text-align: center;
    box-shadow: 0 4px 12px var(--shadow-color);
}

@media screen and (max-width: 600px) {
    body {
        padding: 16px;
    }

    .page-header h1 {
        font-size: 1.8rem;
    }

    .catalog-admin-link {
        position: static;
        display: inline-block;
        margin-top: 12px;
    }
}