body {
    font-family: Arial, sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
}

.container {
    text-align: center;
    border: 2px solid black;
    padding: 20px;
    border-radius: 10px;
}

#kennzeichen-form {
    display: flex;
    flex-direction: column;
}

input, button {
    margin: 10px 0;
}

.valid {
    background-color: green;
}

.invalid {
    background-color: red;
}