On the homepage of the Kingdom Wiki, the options change when hovered over. I can't figure out how it works, I can't replicate the source code. How can I recreate it? (Kingdom wiki linked)
Basically they have two images for each button, one frozen and one animated , and then a CSS rule that switches between the images when the button is hovered. The coding is simple here but you need to have the images you want or knowing what else you want to change when hovered (color, size, jumping up-down, etc.)
Not necessarily, the browser knows how to resize images. But they better at least fit the shape - better don't put a rectangular image on a square button.