html,body {
    margin: 0;
    height: 100vh
}

body {
    font-family: sans-serif;
    color: #fff;
    background: black;
    display: flex;
    justify-content: center;
    align-items: center
}

a {
    color: inherit
}

#demo-select {
    position: absolute;
    top: 10px;
    left: 10px
}

#source {
    position: absolute;
    top: 10px;
    right: 10px
}