How to set background image in Flet (Flutter) in Python

Question

Can anyone help me in this problem? I want set the background image of a flet app (frameless) The results must look like this:

Before

Before

After (Expectations)

After

I was in hurry so this is not properly edited. (I don't have much repuations in this StackOverflow Account So I can't attach image directly) I tried to use ft.Container's image_src parameter but didn't work.