Example 1: Simple SVG

HTML

<svg viewBox="0 0 200 200" xmlns="http://www.w3.org/2000/svg">
  <defs>
    <filter id="dilate">
      <feMorphology operator="dilate" in="SourceGraphic" radius="2" />
    </filter>
    </defs>
 <rect x="10" y="10" width="50" height="50" fill="none" stroke-width="5" stroke="black"/>
 <rect x="10" y="60" width="50" height="50" fill="none" stroke-width="5" stroke="black"/>
 <rect x="60" y="10" width="50" height="50" fill="none" stroke-width="5" stroke="black"/>
 <rect x="10" y="10" width="50" height="50" fill="#cccc99" filter="url(#dilate)"/>
 <rect x="60" y="10" width="50" height="50" fill="#cccc99" filter="url(#dilate)"/>
 <rect x="10" y="60" width="50" height="50" fill="#cccc99" filter="url(#dilate)"/>
</svg>