The Sass code should use @extend [1] instead of @mixin, which doesn't insert the whole definition each time but extends the base definition: .island, .head

The Sass code should use @extend [1] instead of @mixin, which doesn't insert the whole definition each time but extends the base definition: .island, .header, .content { display block; … } [1]: http://sass-lang.com/docs/yardoc/file.SASS_REFERENCE.html#extend http://sass-lang.com/docs/yardoc/file.SASS_REFERENCE.html#ex...