It looks like linear gradient url is the problem. I think this is an upstream issue in the example, as embedding a fill by ID can break if the ID is listed multiple times on the page (which is the case here since this icon is always used at least twice)

Maybe changing it upstream to something like that

<path d="m99.75 67.469c-28.032 etc..." fill="url(#g1)"/>
<defs>
  <linearGradient id="g1" x1="55.549" x2="110.15" y1="77.07" y2="131.85" gradientUnits="userSpaceOnUse">
    <stop stop-color="#387eb8"/>
    <stop stop-color="#366994" offset="1"/>
  </linearGradient>
</defs>

could help?

Originally posted by @krassowski in jupyterlab/plugin-playground#218 (comment)