Hi there!
I found out that there are some quirks when editing SCSS in Sublime Text 3:
Using the Sass package and setting the syntax to Sass > SCSS, then there are many basic autocompletes missing.
When using the SCSS package, then there are some properties displayed in a strange way or even marked as wrong (especially for display: flex):
As I’m new to Sublime Text (switched from Atom), maybe anyone can suggest me the best setup for editing SCSS?
Thank you!
Michael
Get the rewrite branch of the fork
https://github.com/braver/Syntax-highlighting-for-Sass/tree/rewrite
Thanks @andremacola, that works pretty well! 
Okay, so I managed to install the ‘rewrite’ branch manually by downloading the ZIP and extract it to my Packages folder. Is this the way you do it? I couldn’t get Package Control to install it, though I’ve added the URL of that branch as a repository. Sorry for asking again.
Yes. This is a fork from another outdated Sass package. I think braver added to package control recently with the name SublimeSass