body {
    margin: 0;
    padding: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #000;
    overflow: hidden;
}

.game-container {
    position: relative;
}

#gameCanvas {
    background-color: #111;
    border: 2px solid #444;
}

.score {
    position: absolute;
    top: 10px;
    right: 10px;
    color: #fff;
    font-family: Arial, sans-serif;
    font-size: 20px;
    z-index: 1;
}

.player {
    width: 50px;
    height: 50px;
    position: absolute;
    background: url('我方飞机.png') no-repeat center center;
    background-size: contain;
}

.enemy {
    width: 50px;
    height: 50px;
    position: absolute;
    background: url('敌方飞机.png') no-repeat center center;
    background-size: contain;
}

#startButton, #restartButton {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    padding: 10px 20px;
    font-size: 20px;
    cursor: pointer;
}

#restartButton {
    display: none;
}

.upgradeButton {
    position: absolute;
    bottom: 10px;
    right: 10px;
    padding: 10px 20px;
    font-size: 16px;
    cursor: pointer;
    display: none;
}

.instructions {
    position: absolute;
    bottom: 10px;
    left: 10px;
    color: #fff;
    font-family: Arial, sans-serif;
    font-size: 16px;
    z-index: 1;
    background-color: rgba(0, 0, 0, 0.5);
    padding: 10px;
    border-radius: 5px;
    max-width: 300px;
}