Shift + Option + Volume keys (⇧+⌥)
All you need to do is to press the Shift and Option keys (⇧+⌥) along with the volume keys, you'll be able to break up each of the bezels into four discrete units. This is something that you can do manually by opening up the system preferences and using the menu bar to get the same result. We find it's much easier to use this shortcut to get the right volume.
Here are two extra tips that are also very useful when an app goes awry. It's good to remember these in case you need to force-quit an app.
Option + Command + Esc (⌥+⌘+esc)
This combination of keys will allow you to force-quit a window, kind of like what PC users do when they bring up the Task Manager in Windows by pressing Control + Alt+ Delete.
Option + Shift + Command + Esc (⌥+⇧+⌘+esc)
In some cases, the previous combination won't work. Sometimes, the foremost window has disappeared. In order to quit this app, use this combination of keys to quit the foremost application.