Apple OS, App, Brightness, Contrast, Volume

Although not tested/validated by Dell, I am using a U3818DW with my MacBook Pro. But have missed the ability to control brightness from the keyboard. This app solved the issue. I also use the Lilu kext to enable sound over mDP.

Finally, for those trying this combo, the Apple EFI Boot display only supports DPv1.1. You need to toggle the protocol by keeping the menu button depressed for 10s while on the DP input option.