Google introduced a sweet hidden menu in Android Marshmallow called the System UI Tuner. It packs a ton of neat little tweaks like hiding status bar icons or showing your battery percentage. You'll then see a message that says System UI Tuner has been added to Settings.
Regarding this, how do I fix system UI?
Press and hold the Home button, Volume buttons and the Power key at the same time. After the Recovery Screen appears, leave all the buttons. Now use Volume button to toggle and Power key to select the 'wipe cache partition'. When the process is complete, select 'Reboot system now' and restart the phone.
How do I turn off the system UI?
With it enabled, you can then tweak your quick toggle tiles, add or remove items from the status bar, and even enter Demo Mode. To turn it back off, tap the action overflow menu from within the System UI Tuner section and choose to turn it off. You can also long-press on the Settings icon again for 5 seconds.
What is Lollipop system UI app?
Partially supported. Android "Lollipop" is a codename for the Android mobile operating system developed by Google, spanning versions between 5.0 and 5.1.1.