What does the '::' selector mean in CSS

Question

I came across a blog-post, where :: was used in their CSS code.

Here is part of their code:

::-webkit-scrollbar {
  width: 10px;
}

The code is working fine for the scrollbar, but I could not find where this selector is defined. What does this officially mean

Answer 1

:: signifies a pseudo-element, as opposed to a pseudo-class :. Pre-CSS3 they both used : and support is a little scrappy for the :: syntax still.

A pseudo-class filters existing elements.

a:link means all <a>s that are :link.

A pseudo-element is a new fake element. div::after create a "fake" element with <div> but after its content.

References

• What is the difference between a pseudo-class and a pseudo-element in CSS?
• Pseudo-element tag info