<svg width="170" height="170" viewBox="0 0 170 170">
  <defs>
    <radialGradient id="radial"
      cx="%" cy="%" fx="%" fy="%" r="%">
      <stop offset="0%" style="stop-color: #f96;"/>
      <stop offset="50%" style="stop-color: #9c9;"/>
      <stop offset="100%" style="stop-color: #906;"/>
    </radialGradient>
   
    </defs>
    <rect x="10" y="10" width="150" height="150"
      style="fill: url(#radial); stroke: black;"/>
  </svg>
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