The 'Problems' tab in Flexbuilder/Eclipse can be very helpful when trying to zero-in on baddies in your code. However, certain types of errors can flood the tab... making it more difficult to keep things straight.

Let's take the 'CSS type selector [X] not processed' error message. If you are working on a styled component, module, or application that doesn't use all of the styles contained within your attached stylesheet... you are going to get these kinds of errors in the problems tab.

Imagine one of these guys for every style that you will use at one point or another - but within the context of the current project aren't. Things can get pretty messy. This is where compiler options can be used to help clean things up a bit.

-show-unused-type-selector-warnings=false

Adding this switch to your 'Additional compiler arguments' as follows:

Click 'OK' to save... and clean/rebuild to remove un-necessary warnings from the problems panel.