参考：
Sass を使いたくなる！便利機能をまとめてみました。| MONSTER DIVE
SASS/Compass で共通ライブラリにしとくと便利なもの – Qiita
Sass 3.2で実装された新機能がヤバい | WebTecNote
4 Sass Features You May Not Have Tried — SitePoint
10 Things You Probably Didn’t Know about Sass – Hacker Noon
Cool things you can do with Sass | Love Huria
Sass brainfuck | Hugo Giraudel
The Double Ampersand Selector | Treehouse Blog
HugoGiraudel/awesome-sass: A curated list of awesome Sass – GitHub