[css] Is there a way to use SVG as content in a pseudo element :before or :after

Yes you can! Just tested this and it works great, this is awesome! It still doesn't work with html, but it does with svg.

In my index.html I have:

<div id="test" style="content: url(test.svg); width: 200px; height: 200px;"></div>

And my test.svg looks like this:

<svg xmlns="http://www.w3.org/2000/svg">
   <circle cx="100" cy="50" r="40" stroke="black" stroke-width="2" fill="red"/>
   <polyline points="20,20 40,25 60,40 80,120 120,140 200,180" style="fill:none;stroke:black;stroke-width:3"/>
</svg>