This is based on Android N rumors. Let me know how it is. Thank you all!
If you have problems you must update the layers manager app .It isn't the theme.
YOU MUST UPLOAD TO BETA4+ OF LAYERS MANAGER
This is not for CM12.x/13.x but only for rom with RRO/Layers/Overlay. Compatible with Androd Marshmallow and Android N Preview.
HOW TO INSTALL THE THEME:
1) Open layers manager
2) Do one slide down
3) Open N Navbar
4) Select the navbar
5) Choose your favorite home button position and click the fab in the right corner
6) Reboot
THIS WILL ONLY WORK IF YOU HAVE A LAYERS COMPATIBLE CUSTOM ROM AND HDPI,XHDPI,XXHDPI OR XXXHDPI DEVICE.
NOTE:This is not a cm12.x/13.x theme!
YOU NEED ROOT AND LAYERS MANAGER APP INSTALLED
HOW CAN IT USE IT?
1) Install the app.
2) Go to layers manager app.
3) Open N Navbar
4) Install the navbar.
5) Reboot.
HOW TO CHANGE NAVBAR?
1) Uninstall the previous one via layers manager.
2) Install a new one.
3) Reboot.
FAQs:
1) I install the navbar overlay but nothing changes after reboot?
---Make sure that your device is hdpi,xhdpi,xxhdpi or xxxhdpi.
2) Navbars aren't changing?
---unistall the previous one first and also make sure that you have busybox installed.
Special thanks to Crigio and all developers who have advised me!