解决方法
规范声明URL必须指向样式表：
The ‘@import’ rule allows users to import style rules from other style
sheets. Any @import rules must follow all @charset rules and precede
all other at-rules and rule sets in a style sheet. 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.
