.stp-container {
    background: #fff;
    padding: 20px;
    max-width: 500px;
    margin: auto;
    border-radius: 12px;
    box-shadow: 0 0 10px #ccc;
}
.stp-container input, button {
    display: block;
    width: 100%;
    padding: 10px;
    margin-top: 10px;
}