body {
    background-color: #333;
    color: #fff;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
}

.timer-container {
    text-align: center;
    border: 2px solid #555;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 4px 8px rgba(0,0,0,0.5);
}

input, button {
    padding: 10px;
    margin-top: 10px;
    border: none;
    border-radius: 5px;
    font-size: 16px;
    background-color: #555;
    color: #fff;
}

button {
    padding: 10px 20px;
    font-size: 16px;
    cursor: pointer;
    border: none;
    border-radius: 5px;
    background-color: lightgreen; /* フォーカス開始ボタンの色 */
    color: white;
}

button:focus {
    outline: none;
}

button#startButton.active {
    background-color: red; /* フォーカス終了ボタンの色 */
}

button:hover {
    background-color: #777;
}

h1, h2 {
    margin: 10px;
}

#volumeControl {
    margin-top: 15px;
}

#volumeSlider {
    width: 200px;
}