出现
Error: Invalid CSS after " @charset "utf-8"": expected "{", was ";" on line 4 of D:\Git\myproject\loudou140806\loudou140806.github.io\myblog_sass\main.scss
Use --trace for backtrace.
是怎么回事，代码如下：

@charset "utf-8";

// Our variables
$base-font-family: "Helvetica", Arial, sans-serif;
$base-font-size: 16px;
$small-font-size: $base-font-size * 0.875;
$base-line-height: 1.5;

$spacing-unit: 30px;