what is scss

SCSS is a preprocessor which lets you use features that aren’t a part of the wider CSS standard yet, and provides better workflows for maintaining your stylesheets.

With SCSS preprocessor, you can reduce the amount of times you repeat yourself and ensure you’re writing clean, maintainable code for the future.

Scss can take css code and work. 

SCSS is fully compatible with the syntax of CSS, while still supporting the full power of Sass.

Scss is an extension of the syntax of CSS. This means that every valid CSS stylesheet is a valid SCSS file with the same meaning. In addition, SCSS understands most CSS hacks and vendor-specific syntax, such as IE's old filtersyntax. This syntax is enhanced with the Sass features described below. Files using this syntax have the .scss extension.
Dry (dont repeat yourself) code is much better then wet code (write every time).