body {
    font-family: Arial, sans-serif;
    background-color: #f4f4f9;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
}
.container {
    background-color: #fff;
    padding: 20px;
    border-radius: 8px;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
    width: 100%;
    max-width: 500px;
}
h1 {
    margin-top: 0;
    text-align: center;
}
input[type="text"] {
    width: calc(100% - 22px);
    padding: 10px;
    margin: 10px 0;
    border: 1px solid #ddd;
    border-radius: 4px;
    display: block;
    margin-left: auto;
    margin-right: auto;
}
input[type="submit"] {
    padding: 10px 20px;
    background-color: #007BFF;
    color: #fff;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    display: block;
    margin-left: auto;
    margin-right: auto;
}
input[type="submit"]:hover {
    background-color: #0056b3;
}
.result {
    margin-top: 20px;
    padding: 10px;
    border-radius: 4px;
}
.valid {
    background-color: #d4edda;
    color: #155724;
}
.invalid {
    background-color: #f8d7da;
    color: #721c24;
}
.error {
    background-color: #f8d7da;
    color: #721c24;
    padding: 2px 4px;
    border-radius: 4px;
}