JSFiddle - React, Tailwind, and code Playground
HTML
<canvas id="c"></canvas>
<script>x = c.getContext('2d');</script>
JavaScript
d=x.createImageData(w=c.width,h=c.height),e=d.data,W=3*w,A=255
for(j=0;j++<W*h;)X=j%W,Y=j/W|0,E=X-W/2,F=Y-h/2,v=E*E+F*F*9<h*h?A:0,[1].map(f=>{e[(o=j/3|0)*4+3]=A;e[j+o]+=v*f/9})
x.putImageData(d,0,0)