Why not make this truly a lightweight library by calculating and injecting CSS variables in JS on demand once the package gets imported? You could easily shave a few more kilos this way.
I’d be very much surprised if that would save anything; gzip compression is pretty good, but the content-aware compression you’re describing is unlikely to be enough better to compensate for the extra code required. Add to that the downsides (slower loading and a flash of unstyled content) and I’d reckon it a non-starter.
Is it possible to apply for an internship? I'd love to work for this company, but I just got back from the mandatory military service and didn't have a chance to get enough work experience from a real job.