#s2u-flashcards, .s2u-flashcards {
    max-width: 600px;
    margin: 20px auto;
    text-align: center;
}
.s2u-card {
    border: 1px solid #ccc;
    padding: 12px;
    margin: 8px;
    background: #f9f9f9;
    border-radius: 6px;
}
.s2u-hidden {
    display: none;
}
.s2u-lock-message {
    margin-top: 20px;
    font-weight: bold;
}
.s2u-lock-message a {
    color: #008000;
    text-decoration: underline;
}