Select Dropdown: CSS parsing error breaks the editor

CSS does not support inline comments, which makes this line break the editor and throw the following error:

{
  "name": "CssSyntaxError",
  "reason": "Unknown word",
  "source": "\n\tz-index:1000000;;\n\topacity: 1;\n\toutline: none;\n\ttransition: 40ms opacity linear;\n\ttransition-delay: 20ms; // Allows for the popover to reposition without being seen.\n",
  "line": 6,
  "column": 26,
  "message": "<css input>:6:26: Unknown word",
  "input": {
    "line": 6,
    "column": 26,
    "source": "\n\tz-index:1000000;;\n\topacity: 1;\n\toutline: none;\n\ttransition: 40ms opacity linear;\n\ttransition-delay: 20ms; // Allows for the popover to reposition without being seen.\n"
  }
}

When the comment is removed, the error is gone and the page loads normally. Also, notice how this line is appending an extra semicolon ("source": "\n\tz-index:1000000;; (...)). It doesn’t seem to be breaking anything but probably worth addressing as well.

cc @ItsJonQ @sarayourfriend

[ItsJonQ]

Thanks for reporting this @WunderBart !! Will push an update immediately

[fullofcaffeine]

It’s worth documenting here that there’s a suspicion that the culprit might have been related to https://github.com/MohammadYounes/rtlcss. Which is used only when an RTL language is active (i.e., Arabic or Hebrew).