Semantic UI is far from a light-weight CSS framework. I was recently working on a project using semantic, and I saw that the CSS alone was around ~960KB. I'm guessing that something must have been misconfigured for CSS output to be that high just for the Semantic UI framework, but offhand I didn't see it. That didn't include the icon fonts or the JS with Semantic. I'm guessing with some work, that CSS payload could have been trimmed down, but I doubt it could be trimmed enough to be considered light-weight.

I prefer CSS frameworks to provide the bare minimum instead of the kitchen sink. The only exception I make is if I am working on a project that I know will not have design provided. If a project does have a provided design, overriding framework defaults is counterproductive. Just write your own styles when you need them.

I'm using this these days. I find it incredibly flexible.