JSFiddle - React, Tailwind, and code Playground
by jeremyblalock
HTML
<svg width="100%" height="400px">
<defs>
<filter id="myfilter" x="-100" y="-100" width="300" height="300">
<feOffset result="offsetOut" in="SourceAlpha" dx="0" dy="20" />
<feComponentTransfer result="alphaOut" in="offsetOut">
<feFuncA type="linear" slope="0.5" intercept="0" />
</feComponentTransfer>
<feGaussianBlur result="blurOut" in="alphaOut" stdDeviation="20" />
<feBlend in="SourceGraphic" in2="blurOut" mode="normal" />
</filter>
</defs>
<mask id="circleMask" maskUnits="userSpaceOnUse">
<rect fill="#fff" x="0" y="0" width="400" height="400" />
<rect fill="#000" x="20" y="20" width="100" height="100" />
</mask>
<rect x="20" y="20" width="100" height="100" fill="#fff" stroke="none" filter="url(#myfilter)" mask="url(#circleMask)" />
</svg>
CSS
body {
background: #eee;
}