/* Reset and base styles */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    line-height: 1.6;
    color: #333;
    background-color: #f8f9fa;
}

.container {
    max-width: 800px;
    margin: 0 auto;
    padding: 2rem 1.5rem;
}

/* Header */
header {
    text-align: center;
    margin-bottom: 3rem;
    padding-bottom: 2rem;
    border-bottom: 2px solid #dee2e6;
}

header h1 {
    font-size: 2.5rem;
    color: #002654;
    margin-bottom: 0.5rem;
    font-weight: 700;
}

.subtitle {
    font-size: 1.25rem;
    color: #6c757d;
}

/* Language sections */
.lang-section {
    margin-bottom: 2.5rem;
}

.lang-section h2 {
    font-size: 1.75rem;
    color: #002654;
    margin-bottom: 0.5rem;
    padding-bottom: 0.5rem;
    border-bottom: 1px solid #dee2e6;
}

.course-title {
    font-size: 1.1rem;
    color: #495057;
    margin-bottom: 1.5rem;
    font-style: italic;
}

/* Content blocks */
.content-block {
    background: #fff;
    padding: 1.5rem;
    border-radius: 8px;
    margin-bottom: 1.5rem;
    box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
}

.content-block h3 {
    font-size: 1.25rem;
    color: #002654;
    margin-bottom: 1rem;
}

/* Links */
a {
    color: #0066cc;
    text-decoration: none;
    transition: color 0.2s ease;
}

a:hover {
    color: #004499;
    text-decoration: underline;
}

/* Tip box */
.tip {
    background: #e7f3ff;
    padding: 0.75rem 1rem;
    border-radius: 4px;
    font-size: 0.9rem;
    color: #004085;
    margin-bottom: 1rem;
    border-left: 3px solid #0066cc;
}

kbd {
    background: #f8f9fa;
    border: 1px solid #dee2e6;
    border-radius: 3px;
    padding: 0.1rem 0.4rem;
    font-family: monospace;
    font-size: 0.85em;
}

/* Slides list */
.slides-list {
    list-style: none;
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(120px, 1fr));
    gap: 0.75rem;
}

.slides-list li {
    text-align: center;
}

.slides-list a {
    display: block;
    padding: 0.75rem 1rem;
    background: #002654;
    color: #fff;
    border-radius: 4px;
    font-weight: 500;
    transition: background-color 0.2s ease, transform 0.1s ease;
}

.slides-list a:hover {
    background: #003d82;
    text-decoration: none;
    transform: translateY(-1px);
}

.slides-list .disabled {
    display: block;
    padding: 0.75rem 1rem;
    background: #e9ecef;
    color: #868e96;
    border-radius: 4px;
    cursor: not-allowed;
}

/* Section divider */
.section-divider {
    border: none;
    border-top: 1px solid #dee2e6;
    margin: 2.5rem 0;
}

/* Footer */
footer {
    margin-top: 3rem;
    padding-top: 2rem;
    border-top: 2px solid #dee2e6;
    text-align: center;
    color: #6c757d;
    font-size: 0.9rem;
}

footer p {
    margin-bottom: 0.5rem;
}

footer a {
    color: #6c757d;
}

footer a:hover {
    color: #495057;
}

/* Responsive adjustments */
@media (max-width: 600px) {
    .container {
        padding: 1.5rem 1rem;
    }

    header h1 {
        font-size: 2rem;
    }

    .subtitle {
        font-size: 1rem;
    }

    .lang-section h2 {
        font-size: 1.5rem;
    }

    .content-block {
        padding: 1rem;
    }

    .slides-list {
        grid-template-columns: repeat(auto-fill, minmax(100px, 1fr));
        gap: 0.5rem;
    }

    .slides-list a,
    .slides-list .disabled {
        padding: 0.6rem 0.75rem;
        font-size: 0.9rem;
    }
}