What are js hovers for?

Question

css

example - any file on Yandex disk for example

link

https://yadi.sk/d/L8bOPn7O3AV9Js

Screenshot

When hovering on the button "Save to Yandex.disk", the class "button2_hovered_yes" is hung on it and through it the background changes on the before pseudo-element, why is it done this way, and not on css ? If it were not for Yandex, it would be possible to attribute everything to the developer, but in this case, I suppose, the reason is different.

Answer 1

You can not look for a catch, there is none. Everything is very simple and prosaic - this is their native BEM in its purest interpretation. They also use the full BEM stack, not just class name notation. Any style is defined only by the class. Each component is in a separate folder, inside js/css/img, styles are divided into files - block/element/modifier styles are in separate files. All this is assembled by the miracle machine BEM.js.