body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    background-color: #f8f9fa;
}

.submit-btn {
    font-size: 1.5rem;
    border-radius: 30px;
    min-width: 120px;
    padding: 0 2rem;
    height: 66px;
    background: #0d6efd;
    color: white;
    border: none;
    cursor: pointer;
    transition: background 0.3s;
}

.submit-btn:hover {
    background: #0b5ed7;
}

@media (min-width: 768px) {
    .col-md-8.col-lg-6 {
        width: 80%;
        min-width: 300px;
        max-width: 900px;
    }
}

@media (max-width: 768px) {
    .submit-btn {
        font-size: 1.25rem;
        height: 54px;
        min-width: 100px;
    }

    .col-md-8.col-lg-6 {
        width: 100%;
    }
}

/* Stage3 secret 显示使用等宽字体 */
.secret-display {
    font-family: 'Courier New', Courier, monospace;
    font-size: 4em;
    font-weight: bold;
    letter-spacing: 0.05em;
}