Pixbar modifies your device's navigation bar to have solid buttons. This is meant to resemble a certain device that has an exclusive on these kinds of buttons. Currently, Pixbar is meant for phones with stock Lollipop and above. It also is compatible with LG devices. This works without any root permissions needed, as well!
Please note that this app does NOT add a navigation bar if your phone uses physical buttons. It is simply an add-on to those that already have navigation bars.
Support for Xperia and other devices with slightly different navigation buttons will be available in a future release.
NOTE: backgrounds from screenshots are from the Backdrops app. Nova Launcher is the launcher used. Elun icon pack was used in the first screenshot