@Sirhc You probably should have opened with the fact that you are using a variation of @hotNipi's "But it is blue" example theme - Dashboard CSS - custom and blue
That top bar is part of the device display... clock, battery, WiFi, etc.
The same CSS background mod on Android (at least on my v7 phone) is white text on whatever colour the Node-Red theme's Base setting is (I usually use grey for my dark mode).
On an older Android (v4.4), it is always white on black. regardless of Base colour.
And as you noticed, on the iPad (and iPhone?) it is always white on white (when using that CSS background gradient mod), regardless of what Base colour (as tested on my iPad Air 1). It seems to be an Apple thing and I'm not sure you can change it and have a gradient background.