body {
    font-family: Arial, sans-serif;
    background-color: #000;
    color: #fff;
    text-align: center;
    margin: 0;
    padding: 0;
}
header {
    background: #111;
    padding: 20px;
}
nav a {
    color: #fff;
    margin: 0 15px;
    text-decoration: none;
}
.btn {
    display: inline-block;
    background: #fff;
    color: #000;
    padding: 10px 20px;
    margin-top: 20px;
    text-decoration: none;
    font-weight: bold;
}