Answers for "scss include file"

import mixin from another file

@import "../../../theme/main.scss"

sass @use not working

As of 8/2020 @use is only compatible with Dart Sass. 
Check compatibility with documentation.
https://sass-lang.com/documentation/at-rules/use

scss include

// style.scss,  sass will discontinue @include 
@use 'foundation/code';
@use 'foundation/lists';

sass file

Sass is a popular preprocessor scripting language that gets compiled into css. 
There are 2 file extensions:
1) .scss (newer syntax, commonly used)
2) .sass (older syntax with strict indentation)
Learn More at https://sass-lang.com/