What is the difference between :before and ::before?

I just saw a CSS code that included ::before tag. I looked at MDN to see what the ::before is but I really didn't understand it.

Can someone explain how it works?

Does it make a DOM element before what we select by CSS?

Solution 1:

According to those docs, they are equivalent:

element:before  { style properties }  /* CSS2 syntax */

element::before { style properties }  /* CSS3 syntax */

The only difference is that the double colon is used in CSS3, whereas the single colon is the legacy version.

Reasoning:

The ::before notation was introduced in CSS 3 in order to establish a discrimination between pseudo-classes and pseudo-elements. Browsers also accept the notation :before introduced in CSS 2.

Solution 2:

This distinguishes pseudo elements from pseudo classes.

The difference between pseudo classes and pseudo elements is described at http://www.d.umn.edu/~lcarlson/csswork/selectors/pseudo_dif.html