Thanks for reporting this. @jeffw from our support team actually spotted this issue earlier today and I’ve already fixed it. The update will be published tonight or early tomorrow morning.
You can apply the fix now by opening “extensions/theme-utilities/custom-css.php” and replacing line 160 with:
echo stripslashes(htmlspecialchars_decode(get_options_data('options-page', 'custom-styles')));
I hope it’s line 160. I did make a small edit to another part of this file also earlier today and it might have shifted the line number but it should be easy to identify as the last line of code on the page. Thanks.