html,
body,
#jsdos {
    width: 100%;
    height: 100%;
    margin: 0;
    padding: 0;
    background-color: #000;
}

#selection {
    font-family: courier, monospace;
    color: #fff;
    position: fixed;
    z-index: 1;
    width: 750px;
    padding: 30px;
    font-size: 18px;
}

button {
    width: 10%;
    height: 10%;
    font-size: inherit;
}