boundaries.svg

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE svg PUBLIC 
    "-//W3C//DTD SVG 1.0//EN" 
    "http://www.w3.org/TR/2001/REC-SVG-20010904/DTD/svg10.dtd">
<svg version="1.0" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" 
     height="320" width="640px"
     xml:space="preserve">

  <defs>
    <radialGradient id="grad1" cx="50%" cy="50%" r="50%" fx="50%" fy="50%">
      <stop offset="  0%" style="stop-color:rgb(0,0,0); stop-opacity:1" />
      <stop offset="100%" style="stop-color:rgb(255,255,255); stop-opacity:0" />
    </radialGradient>
  </defs>
  <circle cx="160" cy="160" r="128" stroke="black" stroke-width="16px" fill="white"/>
  <circle cx="480" cy="160" r="160" fill="url(#grad1)" />
</svg>