body {
    background-color: #000000;
    color: #FFD700;
    font-family: 'Noto Serif JP', serif;
    text-align: center;
    margin: 0;
    padding: 20px;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

.container {
    max-width: 600px;
    margin: 0 auto;
    flex: 1;
}

h1 {
    font-size: 2.5em;
    margin-bottom: 10px;
}

.book-link {
    margin-bottom: 20px;
}

.book-link a {
    color: #FFD700;
    text-decoration: none;
    font-size: 0.8em;
}

hr {
    width: 100%;
    border: 0;
    border-top: 1px solid #FFD700;
    margin-top: 0;
}

button {
    background-color: #FFD700;
    color: #000000;
    border: 2px solid transparent;
    padding: 10px 20px;
    font-size: 1.2em;
    cursor: pointer;
    margin-top: 20px;
    border-radius: 10px;
    transition: background-color 0.3s, border-color 0.3s;
    font-weight: bold;
}

.initial-image {
    max-width: 100%;
    height: auto;
    margin: 20px auto;
    display: block;
}

button:hover {
    background-color: #B8860B; /* 暗い金色 */
    border-color: #FFD700;
}

footer {
    margin-top: 40px;
    font-size: 0.7em;
    color: #888888;
}

#result {
    margin-top: 30px;
}

ruby rt {
    font-size: 0.5em;
}

#fortune-image {
    max-width: 100%;
    height: auto;
    margin: 20px 0;
    opacity: 0;
    transition: opacity 1.5s ease-in-out;
}

#fortune-image.fade-in {
    opacity: 1;
}

.hidden {
    display: none;
}

@media (max-width: 768px) {
    h1 {
        font-size: 2em;
    }
}

@media (max-width: 480px) {
    h1 {
        font-size: 1.5em;
    }

    button {
        font-size: 1em;
    }
}