Parsing regression

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In version v0.9.31 i have noticed the following error:

SyntaxError: Failed to execute 'insertRule' on 'CSSStyleSheet': Failed to parse the rule '\--sxs{--sxs:6}'.

I have a valid CSS code in the following format:

\--selector{--variable:1}

note that the double-dash is escaped to make it a valid CSS.

This used to work in versions prior to 0.9.31, probably the issue is caused by changes in f29c634.

I am aware that my use-case is probably a bit niche/awkward, but i require it and given it's a valid CSS, i'd really appreciate if this could be accounted for 🙏