What other thing can I do with "before" and "after" pseudo element?

Question

I came to know that this (mentioned in question) CSS pseudo elements are used to insert some contents before & after HTML elements. The Syntex is

element::before {
content: "";
}

But, what does it do if I use like this ?

element::before{
content: "";
padding: 0px;
margin: 0px;
box-sizing: border-box;
}

/* Sorry for bad English */

Answer 1

element:: before is the original appearance of the element however if you used element:: after, the appearance of the original element will change

Answer 2

it is similar in using hover function