CSS animation.

I ran into a little bit of a problem with the VS-code live sass compiler toward completing this challenge. All my SASS files where compiled successfully but suddenly it stopped compiling one SASS file but for the others, it was working just fine. I was hoping I could get some help on this.

Also, which way to compile sass is most preferred between using extensions like 'live sass compiler' or apps like 'prepros' ? And if apps then which ones do you recommend I start using?