* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: 'Arial', sans-serif;
    background-color: #f0f0f0;
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
}

.container {
    text-align: center;
    padding: 20px;
    background-color: #fff;
    border-radius: 10px;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    width: 90%;
    max-width: 400px;
}

h1 {
    font-size: 24px;
    margin-bottom: 20px;
}

input {
    width: 80%;
    padding: 10px;
    font-size: 16px;
    margin-bottom: 10px;
    border: 2px solid #ccc;
    border-radius: 5px;
}

button {
    padding: 10px 20px;
    font-size: 16px;
    background-color: #4CAF50;
    color: white;
    border: none;
    border-radius: 5px;
    cursor: pointer;
}

button:hover {
    background-color: #45a049;
}

.error-message {
    color: red;
    margin-bottom: 10px;
    font-size: 16px;
    visibility: hidden; /* 初期状態では非表示 */
}

@media (max-width: 600px) {
    .container {
        width: 80%;
        padding: 15px;
    }

    h1 {
        font-size: 20px;
    }

    input {
        width: 90%;
    }

    button {
        width: 90%;
    }
}