adding pseudo elements to css code example

Example 1: pseudo elements css

::after 	Matches a stylable element appearing after the originating element's actual content.
::before 	Matches a stylable element appearing before the originating element's actual content.
::first-letter 	Matches the first letter of the element.
::first-line 	Matches the first line of the containing element.
::grammar-error 	Matches a portion of the document containing a grammar error as flagged by the browser.
::marker 	Matches the marker box of a list item, which typically contains a bullet or number.
::selection 	Matches the portion of the document that has been selected.
::spelling-error 	Matches a portion of the document containing a spelling error as flagged by the browser.

Example 2: css pseudo classes

button/anchor:hover / :active / :checked
:nth-of-type(3) // select the third element
:nth-of-type(3n) // select an element every three