What is the implementation of bootstrap smooth tabs?

Question

css

Reason for the question: I am doing my own implementation of changing blocks (like how tabs are changed in bootstrap), I don’t use them and it makes sense. I also know how they work, but the question is: how do they actually implement the use of .active and .fade.in ?
After all, fade gives us just a change opacity, while it .activesets for an element, if you set classes to a block in this way, then it just changes from to , without playing the fade animation, this thing could just be solved with the usual ones , but I would like to know how this moment bypassed in bootstrap tabs. display:block;display:nonedisplay:block.fadeIn(), fadeOut()

Answer 1

in bootstrap fade effect is achieved by adding two classes on toggle.
First, .active is added (we display the block), then .show (removes the opacity: 0 property)