I used Semantic-UI and was really impressed but its size was a show-stopper for me. Another thing is although it looks good on desktops, mobile often seems like an afterthought and they do not even have a responsive menu, which means you have to write two menus or resort to some hack if you need a mobile-friendly menu. This issue has been open for forever and the authors have yet to come up with a favorable response. I've since switched to Bootstrap 4 alpha and I'm looking to jump to Bulma now due to some limitations.
You can compile it to include only the components you actually use. I don't use stock semantic myself. I use the react port which is a separate project which uses just the CSS of the semantic library (and again can be compiled to include the css/theme you want).
I've never heard of bulma until this post so I will give it a look.
