:root {
    --bg-dark: #2c2c2c;
    --text-light: #f5f5f5;
    --board-light: #f0d9b5;
    --board-dark: #b58863;
    --accent: #4a8b51;
    --accent-hover: #3a6b40;
}

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

body {
    font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
    background-color: #f9f9f9;
    color: #333;
    line-height: 1.6;
}

.app-header {
    background-color: var(--bg-dark);
    color: var(--text-light);
    padding: 1rem 2rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

.progress-badge {
    background: var(--accent);
    padding: 0.3rem 0.8rem;
    border-radius: 20px;
    font-size: 0.85rem;
    font-weight: bold;
}

.app-layout {
    display: flex;
    flex-direction: column;
    max-width: 1200px;
    margin: 2rem auto;
    gap: 2rem;
    padding: 0 1rem;
}

@media (min-width: 768px) {
    .app-layout { flex-direction: row; }
    .board-section { flex: 2; }
    .lesson-section { flex: 1; }
}

.status-bar {
    text-align: center;
    font-size: 1.2rem;
    font-weight: bold;
    margin-bottom: 1rem;
    color: var(--bg-dark);
}

.controls {
    display: flex;
    justify-content: center;
    gap: 1rem;
    margin-top: 1.5rem;
}

.btn {
    background-color: var(--accent);
    color: white;
    border: none;
    padding: 0.8rem 1.5rem;
    border-radius: 8px;
    cursor: pointer;
    font-weight: bold;
    transition: background 0.3s ease;
}

.btn-secondary { background-color: #666; }
.btn:hover { background-color: var(--accent-hover); }

.lesson-section h2 { margin-bottom: 1rem; border-bottom: 2px solid #ddd; padding-bottom: 0.5rem; }

.lesson-card {
    background: white;
    padding: 1.5rem;
    border-radius: 12px;
    box-shadow: 0 4px 6px rgba(0,0,0,0.05);
    margin-bottom: 1rem;
    border-left: 5px solid var(--accent);
}

.lesson-card.locked {
    opacity: 0.6;
    border-left-color: #aaa;
    background: #e9e9e9;
}