percentage-transform-fractional-box-size.html

<!doctype HTML>
<style>
.container {
  position: absolute;
  top: 0px;
  left: 0px;
  width: 303px;
  height: 303px;
  background-color: #ccc;
}

.child {
  width: 10%;
  height: 10%;
  background-color: #333;
  transform: translate(900%, 900%);
}
</style>
<div class="container">
  <div class="child"></div>
</div>

chromium/third_party/blink/web_tests/paint/transforms/percentage-transform-fractional-box-size.html