Stupid noob question. How do such graphics work in browser games?

Urka

Sorry for the stupid question. I'm a total noob. What is this animation that is usually used in browser games? I mean the slight movements of the knight and the highlights on the icons in the attachment. Is it a gif? Or maybe a video? Why can't I view these media files in the browser console? How does it work? How is it optimized? I'm trying to make an animation for a website, but it's very large, and I think I'm doing it all wrong.

I would appreciate any information about this.

Materials taken from the game Total Battle

Muzzoid

Browser games these days are these day mostly done using webgl, which is low level GPU stuff. they do not tend to be built out of web elements, but rather built in traditional game engines and exported to the web.
Unity, unreal and godot can all export to web.
BUT if you want just some 2d animation stuff for a website, Lottie may be your answer. https://lottiefiles.com/
It was originally an after effect plugin, but now there are specific lottie editors.