Sass is what CSS should be. It adds variables, nesting, mixins and more to regular CSS.
CodeKit compiles Sass files into CSS files.
First, make sure you've read Setting Language Options.
To set options for all Sass files in a project simultaneously, open Project Settings and choose the Sass category under Languages. To change options for just one file, select it and use the inspector pane shown above.
Choose Compressed for the smallest CSS files. The other options yield pretty-printed CSS, but you don't need that because you'll use source maps.
This should be None. Otherwise, selectors in your CSS file will have comments telling you where they came from in your Sass file. You don't need this because you'll use source maps.
This places a *.map file next to the compiled CSS. Browsers use this file to show you the original Sass code in the web inspector instead of the compiled CSS.
Autoprefixer & Bless
Output Path & Action
These options apply to files of all types. They are explained in Setting Output Paths & Actions.
Sass files can import other files. To view these relationships, click the Linked Files tab:
At the top, this pane shows all files that your selected Sass file imports. Below that are all the files that import the one you have selected. If you see [FW] after the filename, that file is part of a CodeKit Framework
The _Partial Convention
If a filename starts with an underscore, CodeKit automatically sets the Output Action for that file to Ignore. These files are known as "partials"; they are meant to be imported into other files rather than compiled on their own.
CodeKit supports Sass "import globbing". If you write @import 'someFolder/*', all Sass files in someFolder will be imported in alphabetical order. You can also use multi-level globbing such as folder/**/*, which imports all Sass files in 'folder' and in any subfolders thereof.
Warning: Variables in Import Statements
Sass allows you to use variables in @import statements. However, doing so makes it impossible for CodeKit to determine links between your files. The variable is not resolved until the file is actually compiled and CodeKit does not compile while scanning for @import statements because that would be slow.
If you use variables in import statements, your file will still compile just fine. But "dependent" files won't. Normally, if File 1 imports File 2, when you save File 2, CodeKit will go compile File 1 because an imported file has changed. When you use variables in import statements, CodeKit won't be aware of the link between these files.