Answers for "include scss"

import mixin from another file

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

sass mixin

@mixin transform($property) {
  -webkit-transform: $property;
  -ms-transform: $property;
  transform: $property;
}
.box { @include transform(rotate(30deg)); }

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/