body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background: linear-gradient(to bottom, #87CEEB, #E0F6FF); /* 青空っぽいグラデーション */
    overflow: hidden;
    margin: 0;
}

.game-area {
    position: relative;
    width: 300px;
    height: 500px;
    background: linear-gradient(to bottom, #fff8dc, #ffefd5); /* やさしいクリーム色のグラデーション */
    border: 3px solid black;
    border-radius: 10px;
    box-shadow: 5px 5px 15px rgba(0, 0, 0, 0.2);
    overflow: hidden;
}

/* 背景にふんわりした雲のエフェクト */
.game-area::before {
    content: "";
    position: absolute;
    width: 100%;
    height: 100%;
    background: radial-gradient(circle at 30% 20%, rgba(255, 255, 255, 0.5) 10%, transparent 50%),
                radial-gradient(circle at 70% 80%, rgba(255, 255, 255, 0.5) 15%, transparent 60%);
    opacity: 0.8;
}

.container {
    position: absolute;
    left: 50%;
    top: 50%;
    transform: translate(-50%, -50%);
}

#balloon {
    display: block;
    width: 50px;
    height: auto; /* 比率を維持 */
}

#boom-container {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    pointer-events: none;
}

.boom {
    position: absolute;
    width: 50px;
    height: auto;
    animation: explode 0.5s ease-out;
}

@keyframes explode {
    0% { transform: scale(0.5); opacity: 1; }
    100% { transform: scale(1.5); opacity: 0; }
}

/* 風船の揺れアニメーション */
@keyframes shake {
    0% { transform: translateX(0px); }
    25% { transform: translateX(3px); }
    50% { transform: translateX(-3px); }
    75% { transform: translateX(3px); }
    100% { transform: translateX(0px); }
}

#balloon.shake {
    animation: shake 0.3s ease-in-out;
}