How to make a button animation like this?

Question

css

Hello! I'm trying to repeat the button animation as here, on this site https://www.b-reel.com/ Black button in the lower right corner.
I tried to understand through the console - it did not work out very well. The animations are hidden somewhere. Tell me how it is generally arranged? On the console I see - after and before - these are animated layers. But how is it structured in more detail?

Answer 1

animate.css