* {
    box-sizing: border-box;
}

body {
    margin: 0;
    padding: none;
    background-color: #000000;
}

#fullscreen_btn {
    border: 0;
    background: none;
    opacity: .4;
}

/* the canvas *must not* have any border or padding, or mouse coords will be wrong */
#canvas {
    position: absolute;
    aspect-ratio: 800/600;
    max-width: 100%;
    max-height: 100%;
    padding-right: 0;
    display: block;
    border: 0px none;
    visibility: hidden;
    left: 0;
    right: 0;
    top: 0;
    bottom: 0;
    margin: auto;
}