cut holes in svg shapes
<div style="background: #ddf">
<svg width="200" height="200">
<defs>
<mask id="hole">
<rect width="100%" height="100%" fill="white"/>
<circle r="50" cx="100" cy="100" fill="black"/>
</mask>
</defs>
<circle id="donut" r="100" cx="100" cy="100" mask="url(#hole)" />
</svg>
</div>