Page Header Background Settings.

To help you replicate the demo, please install / import the demo content you can see a video of how to do this here:

http://bellevuetheme.com/2015/09/09/wp-booking-system-manage-availability/

If you are trying to add your own custom page header background, try these settings:

http://new.tinygrab.com/6407caa59e6c55314d01725cd003d9642ecc239949.png

Taken from this page (our live demo):

http://demo.themovation.com/bellevue/hotel/explore/

Cheers! :)