This is theme for Stellio Player. https://play.google.com/store/apps/details?id=com.stellio.player
Just install this app and in Stello settings choose Material theme.
Even if you uninstall Stellio, nothing bad will happen. You always can download Stellio Music Player free. Only thing you need is a buy Unlocker. So don't worry :)
If you have any problems or wishes - please contact us stellio.play@gmail.com