body {
    font-family: Arial, sans-serif;
    background-color: #f4f4f4;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
}

#game-container {
    text-align: center;
    max-width: 400px;
    width: 100%;
    position: relative;
}

h1 {
    font-size: 2rem;
    margin-bottom: 10px;
}

#message-area {
    min-height: 50px; /* メッセージ領域の高さを固定 */
    font-size: 1.5rem;
    color: #333;
    margin-bottom: 10px;
    overflow: hidden;
}

#number-display {
    margin: 10px auto;
    position: relative;
}

#number-display img {
    width: 100px;
    height: auto;
}

#next-number-display {
    font-size: 1.5rem;
    color: #555;
    height: 30px; /* 固定高さ */
    display: flex;
    align-items: center;
    justify-content: center;
}

#button-area {
    margin: 20px 0;
}

button {
    padding: 10px 20px;
    margin: 5px;
    font-size: 1.2rem;
    cursor: pointer;
    border: none;
    border-radius: 5px;
    background-color: #007BFF;
    color: white;
    transition: background-color 0.3s;
}

button:hover {
    background-color: #0056b3;
}

#score-area {
    margin-top: 10px;
    font-size: 1.2rem;
}

#history-area {
    margin-top: 20px;
}

#history-images {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 5px;
}

#history-images img {
    width: 50px;
    height: auto;
    border: 2px solid #333;
    border-radius: 5px;
}

/* 特別な正解演出 */
.pop-up {
    animation: pop-up-scale 0.6s ease-in-out;
    background-color: rgba(255, 223, 0, 0.7);
    padding: 10px;
    border-radius: 15px;
    box-shadow: 0 0 20px rgba(255, 223, 0, 1);
}

@keyframes pop-up-scale {
    0% {
        transform: scale(1);
    }
    50% {
        transform: scale(1.3);
    }
    100% {
        transform: scale(1);
    }
}