Web front-end tech breakdown

I've been in the mobile application space as an engineer for awhile and wanted to get a little more up to speed on the tools and techniques used today on web front-ends. Specifically, the more rich and interactive web applications.

What designers and developers are pulling off with what I assume is HTML/CSS/JS is blowing my mind compared to when I last played with this stuff. My goal here is a high level discussion so I'd have a head start on where to begin were I to implement some of these effects and animations myself. Some of this might be just getting familiar with the nomenclature used today.

Let's take this site for example: https://www.everest.agency/

- What are some of the concepts they're using to pull off many of the effects here? There are some 3D effects and transitions - is this done through CSS animations primarily? - What tools/frameworks are commonly used today to facilitate development of a front-end such as this?