Text won’t highlight in Gutenberg

I’ve got an issue and it only happens with one theme which is odd because I don’t think it should affect the backend.
When I’m in Gutenberg and I go to highlight text to bold it, copy it, insert a link, etc, the text doesn’t highlight.
Is there a snippet I can add or a setting I can change (generic to WordPress, I’ve tried contacting the theme dev) to turn on text highlights?

 

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