I love Geany and use it all the time, but I was a bit disappointed to find that CSS extension languages - like Sass, SCSS and Less - don't have syntax highlighting.
@python-megapixel, I have the same problem as you when working with SASS/SCSS and LESS files, on Geany's [wiki](https://wiki.geany.org/config/scss) you can find the one for SASS, and although it uses the same CSS source type, you can configure some other things, like the compiler and a debugger.
For the moment I leave the [LESS](https://gist.github.com/diazvictor/f5170dc972eda6f06425ca5779f30cb4) one I have. follow the same steps as with the sass file to register this one.
I should also mention this patch for better support. http://geany.robert.dvu.pl/