Can someone point me in the right direction of classes?

Hi!

I'm wondering, how would one achieve something like this:

while hovering over or clicking an element/button it animates and morphs into something else, like a menu.

Let's say I have a button at 150x50px which says something like "click me". If the user clicks it, an animation occurs and the button morphs into a 600x300px menu. click element -> morph into another element with animation.

Now my question is, could I create something like this in javascript and css only? Javascripts onclick (I suppose) and css with it's animation? I've only done the basic css, are there any courses that cover animation?

Thanks