chromium/third_party/blink/web_tests/css3/masking/resources/circle.svg

<svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="360" height="288">
    <rect width="360" height="288" style="fill:rgb(0,0,0)" />
    <circle cx="180" cy="144" r="80" style="fill:rgb(255,255,255)" />
</svg>