Sass is a CSS pre-processor with syntax advancements. Style sheets in the advanced syntax are processed by the program, and turned into regular CSS style sheets. However, they do not extend the CSS standard itself.
CSS variables are supported and can be utilized but not as well as pre-processor variables.
For the difference between SCSS and Sass, this text on the Sass documentation page should answer the question:
The SCSS syntax uses the file extension
.scss. With a few small exceptions, it’s a superset of CSS, which means essentially all valid CSS is valid SCSS as well. Because of its similarity to CSS, it’s the easiest syntax to get used to and the most popular.
The indented syntax was Sass’s original syntax, and so it uses the file extension
.sass. Because of this extension, it’s sometimes just called “Sass”. The indented syntax supports all the same features as SCSS, but it uses indentation instead of curly braces and semicolons to describe the format of the document.
However, all this works only with the Sass pre-compiler which in the end creates CSS. It is not an extension to the CSS standard itself.
Answer from anon on Stack OverflowVideos
Sass is a CSS pre-processor with syntax advancements. Style sheets in the advanced syntax are processed by the program, and turned into regular CSS style sheets. However, they do not extend the CSS standard itself.
CSS variables are supported and can be utilized but not as well as pre-processor variables.
For the difference between SCSS and Sass, this text on the Sass documentation page should answer the question:
The SCSS syntax uses the file extension
.scss. With a few small exceptions, it’s a superset of CSS, which means essentially all valid CSS is valid SCSS as well. Because of its similarity to CSS, it’s the easiest syntax to get used to and the most popular.
The indented syntax was Sass’s original syntax, and so it uses the file extension
.sass. Because of this extension, it’s sometimes just called “Sass”. The indented syntax supports all the same features as SCSS, but it uses indentation instead of curly braces and semicolons to describe the format of the document.
However, all this works only with the Sass pre-compiler which in the end creates CSS. It is not an extension to the CSS standard itself.
I'm one of the developers who helped create Sass.
The difference is syntax. Underneath the textual exterior they are identical. This is why sass and scss files can import each other. Actually, Sass has four syntax parsers: scss, sass, CSS, and less. All of these convert a different syntax into an Abstract Syntax Tree which is further processed into CSS output or even onto one of the other formats via the sass-convert tool.
Use the syntax you like the best, both are fully supported and you can change between them later if you change your mind.
A.K.A Python but CSS vs JavaScript but CSS