Check out example codes for ":: after css". It will help you in understanding the concepts better.

Code Example 1

/* Description:
The ::after selector inserts something after the content of each 
selected element(s) (ie: after <p> tag or .addEndingText class).*/

/* Example: 
Insert some text after the content of each <p> element:*/
p::after { 
  content: " - Remember this";
}

/*NOTE: IE8 and Opera 4-6 only support the old, single-colon CSS syntax 
(:after). Newer versions support the standard, double-colon syntax 
(::after).*/

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