Error: Invalid CSS after "$clr-link": expected selector or at-rule, was ":              ..."
       on line 21 of D:/Git/myproject/loudou140806/loudou140806.github.io/myblog/sass/_setting-colors.scss
       from line 10 of D:\Git\myproject\loudou140806\loudou140806.github.io\myblog\sass\screen.scss
 Use --trace for backtrace.

$clr-contrast:          #D0648A;  // red

$clr-link:              $clr-contrast;

这样写为什会报错