Reply To: How do we pop up a new "section" onto a page like gmail? (SOLVED)

[Beverleyh]

Interactive functionality (e.g. click a button to trigger an action) normally comes under the umbrella of JavaScript; maybe via the addition/removal of a class that in turn triggers something to happen in either CSS or JavaScript, so maybe start your research there.

For a CSS-only method, have a look in to the checkbox hack https://css-tricks.com/the-checkbox-hack/. It isn’t as versatile as JavaScript would be, and depends heavily on element placement in the DOM, but it might be an option for you.