继承时报错找不到类

为什么继承时报错 找不到类  引入了iconfont. css也不行

Error: ".toolbar .weixin .toolbar-btn" failed to @extend ".icon-weixin".
      The selector ".icon-weixin" was not found.
      Use "@extend .icon-weixin !optional" if the extend should be able to fail.
       on line 178 of F:\web\study\tollbar\styles\toolbar3.scss
 Use --trace for backtrace.