Tutoring web design, you deal with nuances. The tutor tells a quick trick for when fine tuning is needed.

If two rules appear like so

element{color:red}
element{color:green}

the element will be green (in my experience, anyway). That is, the later rule will be expressed.

Therefore, when a person has a style sheet with many elements sharing the same rule

e1,e2,e3,e4,e5{color:red}

but only wants to change one of them, they can specify the one to change in a later rule

e3{color:blue}

HTH:)

Source:

Meyer, Eric A. CSS Pocket Reference. Sebastopol: O’Reilly Media, Inc., 2004.

CSS: fine tuning by later reference