body {
    background: #000;
    color: #0ff;
    font-family: monospace;
    text-align: center;
    padding: 5em;
}
#core {
    border: 2px solid #0ff;
    padding: 2em;
    display: inline-block;
}
button {
    background: #0ff;
    border: none;
    padding: 1em 2em;
    color: #000;
    cursor: pointer;
    font-weight: bold;
}