The CSSImportRule interface represents a @import rule is
used to import style rules from other style sheets.
The location of the style sheet to be imported. The attribute will not
contain the "url(...)" specifier around the URI.
A list of media types for which this style sheet may be used.
The style sheet referred to by this rule, if it has been loaded. The
value of this attribute is null if the style sheet has not
yet been loaded or if it will not be loaded (e.g. if the style sheet is
for a media type not supported by the user agent).