src/assets/stop-icon-shadow-64.svg
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" version="1.1" baseProfile="full" viewBox="-2 -2 72 72" height="64" width="64">
<style>
.heavy { font: bold 32px sans-serif; color:purple; }
</style>
<defs>
<filter id="f1" x="0" y="0">
<feGaussianBlur in="SourceGraphic" stdDeviation="3" />
</filter>
</defs>
<mask id="myMask">
<rect x="0" y="0" width="100" height="100" fill="white" />
<text text-anchor="middle" x="34" y="46" stroke-width="1.5" stroke="black" fill="black" class="heavy">H</text>
</mask>
<g filter="url(#f1)" opacity="0.5">
<rect x="-10" y="-10" width="100" height="100" fill="white" opacity="0"/>
<circle cx="34" cy="34" r="32" stroke="black" stroke-width="1" fill="black" mask="url(#myMask)"/>
</g>
</svg>