HTML
<div class='box'>
<svg>
<mask id='m' fill='#fff'>
<rect id='r' width='100%' height='100%'/>
<circle id='c' r='50' fill='#000'/>
<use xlink:href='#c' x='100%'/>
<use xlink:href='#c' y='100%'/>
<use xlink:href='#c' x='100%' y='100%'/>
</mask>
<use xlink:href='#r' fill='slateblue' mask='url(#m)'/>
</svg>
</div>
