A URI value (
<uri>) is a
reference to a file such as a graphic or another style sheet. CSS defines
a URI as relative to the style sheet that contains it. URI stands for
Uniform Resource Identifier, which is the more recent name for URLs.
(Technically, URLs are a subset of URIs.) In CSS, which was first defined
when URIs were still called URLs, this means that references to URIs will
actually appear in the form