Hm. When I tried this on my site it retained a debugging element that is decidedly not required, but adds a lot of bytes to the CSS:
body::after{display:none;content:"";background-image:url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='1' height='29'><rect style='fill: rgb(196,196,196);' width='1' height='0.25px' x='0' y='28'/></svg>");position:absolute;top:23px;left:0px;z-index:9998;opacity:1;width:1425px;height:3693px;background-size:auto 1.414rem;background-position-y:0.6rem}