help !!

does anyone know how i can make the small background a bit transparent without making all the text and pics/ gifs/ blinkies transparent too? 

i want to be able to see the forest background a bit on the mobile app but It doesn't show so I want to make the small background a bit transparent to see it a bit

idk if I'm explaining myself properly but yea

I tried to change the opacity but it changes it for everything and I'm going insane