canvas {
    display: block;
    margin: auto;
    background-color: #1f1f1f;
}

#playbutton {
    width: 100px;
    height: 50px;
    display: block;
    margin: auto;
    margin-top: 10px;
    font-family: Arial, sans-serif;
    font-size: 30px;
    color: #b1da0b;
    font-weight: bold;
    background-color: #343437;
    cursor: pointer;
    position: absolute;
    top: 45%;
    left: calc(47%);
}

* { margin:0; padding:0; } /* to remove the top and left whitespace */

html, body { width:100%; height:100%; } /* just to be sure these are full screen*/

canvas { display:block; } /* To remove the scrollbars */