body {
    max-width: 1200px;
    margin: 0 auto;
    padding: 25px 20px;
    background: linear-gradient(135deg, #f5f7fa 0%, #c3cfe2 100%);
    min-height: 100vh;
}

h1 {
    color: #2c3e50;
    margin-bottom: 20px;
    font-size: 2rem;
    font-weight: 700;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    letter-spacing: -0.5px;
}

.back-btn {
    display: inline-block;
    margin-bottom: 20px;
    padding: 9px 18px;
    background-color: #34495e;
    color: white !important;
    border-radius: 8px;
    text-decoration: none !important;
    font-weight: 500;
    font-size: 0.95rem;
    transition: all 0.3s ease;
    box-shadow: 0 2px 8px rgba(0,0,0,0.1);
}

.back-btn:hover {
    background-color: #2c3e50;
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(0,0,0,0.15);
}

.game-container {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 20px;
    margin-top: 0;
}

.game-info {
    background: white;
    border-radius: 14px;
    padding: 25px;
    box-shadow: 0 4px 20px rgba(0,0,0,0.08);
    width: 100%;
    max-width: 600px;
}

.game-controls {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
    flex-wrap: wrap;
    gap: 10px;
}

.mode-selector {
    display: flex;
    gap: 10px;
}

.mode-btn {
    padding: 8px 16px;
    border: 2px solid #3498db;
    background: white;
    color: #3498db;
    border-radius: 6px;
    cursor: pointer;
    font-size: 14px;
    transition: all 0.2s;
}

.mode-btn.active {
    background: #3498db;
    color: white;
}

.mode-btn:hover {
    background: #2980b9;
    color: white;
    border-color: #2980b9;
}

.difficulty-selector {
    display: none;
    margin-top: 15px;
    padding-top: 15px;
    border-top: 1px solid #ecf0f1;
}

.difficulty-selector.show {
    display: block;
}

.difficulty-label {
    font-size: 14px;
    color: #7f8c8d;
    margin-bottom: 10px;
    font-weight: 500;
}

.difficulty-buttons {
    display: flex;
    gap: 8px;
    flex-wrap: wrap;
}

.difficulty-btn {
    padding: 6px 14px;
    border: 2px solid #27ae60;
    background: white;
    color: #27ae60;
    border-radius: 6px;
    cursor: pointer;
    font-size: 13px;
    transition: all 0.2s;
}

.difficulty-btn.active {
    background: #27ae60;
    color: white;
}

.difficulty-btn:hover {
    background: #229954;
    color: white;
    border-color: #229954;
}

.reset-btn, .undo-btn {
    padding: 8px 16px;
    background: #e74c3c;
    color: white;
    border: none;
    border-radius: 6px;
    cursor: pointer;
    font-size: 14px;
    transition: background 0.2s;
}

.reset-btn:hover, .undo-btn:hover {
    background: #c0392b;
}

.undo-btn {
    background: #95a5a6;
}

.undo-btn:hover {
    background: #7f8c8d;
}

.undo-btn:disabled {
    background: #bdc3c7;
    cursor: not-allowed;
}

.status {
    text-align: center;
    font-size: 18px;
    font-weight: 600;
    color: #2c3e50;
    margin: 10px 0;
}

.board-container {
    background: white;
    border-radius: 12px;
    padding: 20px;
    box-shadow: 0 4px 15px rgba(0,0,0,0.05);
    display: inline-block;
}

#board {
    border: 2px solid #2c3e50;
    display: block;
    cursor: pointer;
    background: #deb887;
}

/* 移动端优化 */
@media (max-width: 767.98px) {
    body {
        padding: 15px 12px;
    }
    
    .back-btn {
        margin-bottom: 15px;
        padding: 7px 14px;
        font-size: 0.85rem;
    }
    
    .game-info {
        padding: 20px;
        border-radius: 12px;
    }
    
    .board-container {
        padding: 15px;
    }
    
    #board {
        width: 100% !important;
        max-width: 100%;
    }
}