css conversion error with github pages

I'm after some help with an error that I'm running into when trying to build for github-pages:

Conversion error: Jekyll::Converters::Scss encountered an error while converting 'assets/css/main.scss':
                    Invalid CSS after "...in-bottom: math": expected ";", was ".div($spacing-u..." on line 45

This seems to stem from one of the yat theme css files here and possibly others from the recent commit:

/tmp/jekyll-remote-theme-20241013-12540-3ng7gr/_sass/yat/_base.scss:45: Invalid CSS after "...in-bottom: math": expected ";", was ".div($spacing-u..." (Sass::SyntaxError)

Apologies if this isn't the source of the error - I think that github pages requires quite an old version of the jekyll-css-converter (I have 1.5.2 installed) which might be in conflict with this deprecation.

Happy to provide more details and post the gemfile as needed. All the files I'm using are here.

Thanks!