<!doctype html>
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1711189">
<div></div>
<script>
  let div = document.querySelector("div");
  let cs = getComputedStyle(div);
  for (let i = 0; i < cs.length; ++i)
    div.style.setProperty(cs[i], cs.getPropertyValue(cs[i]));
  div.style.cssText
</script>