[Bug] Stylebot won't open when ":empty { display: none; }" is present

[lachlanmcdonald]

Stylebot will not open when the page's CSS, or a stylebot override, contains the following CSS:

:empty {
  display: none;
}

This appears to occur due to the way Stylebot is embedded within the page. Embedding the editor as a Web Component might give us the isolation we need to avoid this or other style conflicts.