A page with actual content doesn't need JS to be amped up
I've challenged myself to implement 3 types of useful elements with CSS only, for perl1liner.sourceforge.io documentation.
The blue sidelines give tooltips on where you are (breadcrumbs) and allow deep bookmarking. While the hamburger menu and play button on the code examples use :hover for active functionality. I could even make the humourous post-its wiggle, but haven't implemented that yet.
There's just one regret: the menu doesn't pop back after clicking. You have to push the mouse out again :-(. I wish there was also :hover-unclicked, i.e. active when hovered but inactive again as soon as you click inside. If anybody knows a CSS solution, happy to hear it!
Though that's not the main audience, it's even okish on smart phones without extra effort. Mobile Firefox and Chrome emulate :hover on tap, so even that works. Safari's not so smart, tough luck.