It add types to Javascript, and that makes the code a lot more resistant to stupid errors and its linters are pretty awesome. 

The 900-lbs gorilla of CSS framework world, this one comes with Javascript unlike Bulma. And it has reached such critical mass that there are companies selling bootstrap themes for a price.  For a lot of back-end guys, this or Bulma will give them very clean user interface with minimum effort.

It's CSS framework that provides a lot of classes for your convenience. Also, it's not hard to make custom classes and use them. One big CAVEAT - it does NOT come with any Javascript library, so you need to write JS codes yourself if necessary. Its documentation provides some sample Javascript snippets. 

Forget W3Schools. Use this for looking up definitions and examples of any Javascript functions. 

It allows you to reduce image file size without noticeable loss - not really recognizable by naked eyes. Must have for any web devs.