Yes It is,

What is a project?

Project is simply a series of tasks that need to be completed in order to reach a specific outcome.

you design something which have specific outcome so definitely you can put all your designs in the portfolio. that's it.

Sure. I gues if you can make a ferrari with css you should be able to make some colluns on a website! 😜

I think so. It shows beyond and above skill and manipulation of CSS on top of the fact that they're hard! It takes a long time to learn that and the determination to complete them. I've never been able to make something look decent with CSS art.