it’s hard to tell exactly what causes the second page to go in background without seeing any code. It is definitely possible to make a page slide up and down, just as you want it to be, using Transitions.
I suggest you first create a smaller working example and then see how that differs from what you have in your larger application. Also, if you manage to create a small reproduction that exhibits the problem, please post some code here so we could give it a spin and help you solve it.