When you have compiled your SASS files into valid CSS, an important step is to then test to see that it works. If you start seeing unexpected results, you will want to troubleshoot the CSS code. The trouble is, most browsers don't include support to trace back a SASS-compiled style to its original SASS code; we can fix that (at least for Firefox), by using FireSASS.
For this exercise, you will need a copy of Firefox, with Firebug installed. You can get the latter from http://www.getfirebug.com.