需要将定义变量的文件 @import 进来,而不是 require
详情参考:http://sass-lang.com/tutorial.html 的 @import 段:
@import
Stylesheets can get pretty big. CSS has an @import directive that allows you to break your styles up into multiple stylesheets, but each stylesheet takes a separate (slow) HTTP request. That’s why Sass’s @import directive pulls in the stylesheets directly. Not only that, but any variables or mixins defined in @imported files are available to the files that import them.