chromium/third_party/blink/renderer/core/animation/test_data/svg-smil-animation.html

<svg viewBox="0 0 100 100" xmlns="http://www.w3.org/2000/svg">
  <rect width="10" height="10">
    <animate attributeName="rx" values="0;5;0" dur="1s"/>
  </rect>
</svg>