<svg xmlns="http://www.w3.org/2000/svg">
<defs>
        <mask id="mask" mask-type="alpha">
                <rect width="200" height="200" fill="black" opacity="0"/>
                <rect width="100" height="100" fill="black"/>
                <rect x="100" y="100" width="100" height="100" fill="black"/>
        </mask>
</defs>
<rect width="200" height="200" fill="green" mask="url(#mask)"/>
</svg>