:root {
    --primary-color: #3498db;
    --primary-gradient: linear-gradient(135deg, #3498db, #2980b9);
    --highlight-color: #e74c3c;
    --highlight-gradient: linear-gradient(135deg, #e74c3c, #c0392b);
    --card-bg: #ffffff;
    --card-shadow: 0 8px 20px rgba(0,0,0,0.1);
    --bg-color: #f5f7fa;
    --text-color: #2c3e50;
    --border-radius: 12px;
    --transition-speed: 0.3s;
}

body {
    font-family: 'Microsoft Yahei', Arial, sans-serif;
    margin: 0;
    padding: 0;
    background: var(--bg-color);
    color: var(--text-color);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    overflow-x: hidden;
}

header {
    text-align: center;
    padding: 30px 20px;
    background: var(--primary-gradient);
    color: white;
    box-shadow: 0 4px 12px rgba(0,0,0,0.1);
    border-radius: 0 0 var(--border-radius) var(--border-radius);
    margin-bottom: 40px;
}

header h1 {
    margin: 0 0 20px 0;
    font-size: 2.5rem;
    text-shadow: 2px 2px 4px rgba(0,0,0,0.2);
    letter-spacing: 1px;
}

.controls {
    display: flex;
    gap: 15px;
    justify-content: center;
    margin: 20px 0;
    flex-wrap: wrap;
}

select, button {
    padding: 12px 24px;
    font-size: 16px;
    border: none;
    border-radius: var(--border-radius);
    background: white;
    cursor: pointer;
    box-shadow: 0 4px 8px rgba(0,0,0,0.1);
    transition: all var(--transition-speed) ease;
    font-weight: 500;
}

select {
    background: white url('data:image/svg+xml;utf8,<svg fill="%232c3e50" height="24" viewBox="0 0 24 24" width="24" xmlns="http://www.w3.org/2000/svg"><path d="M7 10l5 5 5-5z"/></svg>') no-repeat right 10px center;
    padding-right: 40px;
    appearance: none;
}

button {
    background: var(--primary-gradient);
    color: white;
    font-weight: bold;
}

button:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 12px rgba(0,0,0,0.15);
}

button:active {
    transform: translateY(0);
}

.game-container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px 40px;
    flex-grow: 1;
}

.game-board {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 40px;
    position: relative;
    perspective: 1000px;
}

.words-column, .meanings-column {
    display: flex;
    flex-direction: column;
    gap: 15px;
    min-height: 600px;
    transition: opacity var(--transition-speed) ease, transform var(--transition-speed) ease;
}

.word-card {
    padding: 20px;
    background: var(--card-bg);
    border-radius: var(--border-radius);
    cursor: pointer;
    transition: all var(--transition-speed);
    text-align: center;
    font-size: 18px;
    user-select: none;
    box-shadow: var(--card-shadow);
    border-left: 4px solid transparent;
}

.word-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 12px 25px rgba(0,0,0,0.15);
    border-left: 4px solid var(--primary-color);
}

.word-card.active {
    background: var(--highlight-gradient);
    color: white;
    transform: scale(1.05);
    box-shadow: 0 10px 20px rgba(231, 76, 60, 0.3);
}

#connection-canvas {
    position: absolute;
    top: 0;
    left: 0;
    pointer-events: none;
    z-index: 1;
    width: 100%;
    height: 100%;
}

.level-display {
    background: var(--highlight-gradient) !important;
    color: white;
    padding: 12px 24px;
    border-radius: var(--border-radius);
    font-size: 16px;
    font-weight: bold;
    box-shadow: 0 4px 12px rgba(231, 76, 60, 0.3);
    animation: pulse 2s infinite;
}

@keyframes pulse {
    0% { transform: scale(1); }
    50% { transform: scale(1.05); }
    100% { transform: scale(1); }
}

@media (max-width: 768px) {
    .game-board {
        grid-template-columns: 1fr;
        gap: 20px;
    }
    
    header h1 {
        font-size: 1.8rem;
    }
    
    .controls {
        flex-direction: column;
        align-items: center;
    }
    
    select, button {
        width: 100%;
        max-width: 300px;
    }
}