If you recently flashed the Android Marshmallow Developer Preview Build 3 to your Nexus device you may have been bummed that the System UI tweaker disappeared. It is actually not gone, but is accessed in a whole new way. If you pull down the notification panel you will notice a gear icon in the top right hand corner, press and hold that gear icon, it will begin to spin, then it will enable your System UI tweaker. This will give you some great options for customizing your Sytem UI. You may find that you need to turn on developer options before this will work. Just head to settings, about phone, software info, click the build number 7 times to unlock dev settings.