Sass 3.2添加了@content指令，它使我们可以将内容块传递到mixin中，如下所示：

 @mixin screen($size) {
  $desktop: "(min-width: 1024px)";
  $tablet: "(min-width: 768px) and (max-width: 1023px)";
  $mobile: "(max-width: 767px)";
  @if $size == desktop {
    @media only screen and #{$desktop} {
      @content;
    }
  }
  @else if $size == tablet {
    @media only screen and #{$tablet} {
      @content;
    }
  }
  @else if $size == mobile {
    @media only screen and #{$mobile} {
      @content;
    }
  }
  @else {
    @media only screen and #{$size} {
      @content;
    }
  }
}


.wrapper {
  margin: 0 auto;
  width: 100%;
  @include screen('tablet') {
    width: 90%;
  }

  @include screen('desktop') {
    width: 85%;
  }
}

如果您有任何疑问，请随时提问。