2.1.19 [CSS-Level2-2009] Section 6.3, The @import rule
The '@import' rule allows users to import style rules from other style sheets. In CSS 2.1, any @import rules must precede all other rules (except the @charset rule, if present). See the section on parsing for when user agents must ignore @import rules. The '@import' keyword must be followed by the URI of the style sheet to include. A string is also allowed; it will be interpreted as if it had url(...) around it.
Quirks Mode (All Versions)
The @import rule is not ignored if it does not precede all other rules (except the @charset rule, if present).
IE8 Mode (All Versions)
@import rules allow invalid characters in font names.
The @import rule is ignored when the print media type is specified.
Quirks Mode, IE7 Mode, IE8 Mode, IE9 Mode and IE10 Mode (All Versions)
@import rules are applied only from style sheets that are linked three levels deep.
A target medium matches a media list if one of the items in the media list is the target medium or 'all'.
Quirks Mode and IE7 Mode (All Versions)
The target medium must match one of the items in the media
all keyword is not supported.