SCSS File is located in the folder src/sass/. SCSS is a CSS preprocessor that adds many features like variables, mixins, imports, color manipulation, functions and tons of other powerful features.
The entire compiler comes in a single class file ready for including in any kind of project in addition to a command line tool for running the compiler from the terminal.
custom.scss - consists of all the custom css code which is used to enhance look and feel of this template
This is a custom css which includes in all the pages and it can be found in css/ i.e custom.css.