Modifying the OS X app Espresso 2 to support syntax highlighting of Sass files is an easy chore. All you need to do is modify the existing CSS plugin to recognize the Sass file extensions ‘sass’ and ‘scss’.
First, find the Espresso 2 plug-in folder, and using the contextual menu (via right-click), choose ‘Show package contents’ for the file CSS.espressoplugin.
Next, within that package, open the file Languages.xml using your preferred text editor.
Last, within this file, add the two lines below to the <detectors> section.
Now re-launch Espresso 2 and you’re good to go!