How can I replace the on screen buttons on my phone?

[Iamaspacellama]

On my Sony Xperia M4 Aqua I recently download an app called twilight which reduces the blue light and overall brightness on the screen. However the band of screen that has the button is completely unaffected by the filter and look horribly when I opens something like Google as there is a band of white exposed as it transitions. Please help
Nikhil
18

 

[Tim1954]

There is a setting on twilight called full screen... Try that, it's right down the bottom under more settings