.styl is the file extension for stylus. Its just another css preprocessor like less or scss http://learnboost.github.io/stylus/ http://learnboost.github.io/st

.styl is the file extension for stylus. Its just another css preprocessor like less or scss http://learnboost.github.io/stylus/ http://learnboost.github.io/stylus/ I think this part is just a typo > So, it has found /assets/style.styl. Now it analyzes extension: > > .sass extension? Use Sass then.