XF 1.2 Background doesnt work

I want to make one giant background for the entire forum. but the resizing is quite a problem. I used vertical repeat, but now it looks like this on short pages (e.g. the help):

I tried all evening with the style properties in HTML, Body and Page Width, but I can't fix it.

Can someone help me please??
Alright :)

My solution was:

Admin CP - Style Properties: General - Body

remove all background settings, just clear all values, so you will have a transparent body-background

Admin CP - Style Properties: General - HTML

Set your background over the HTML settings: (this is important, so that the background always fits the size of the page, not just the size of your (main page body)

image: background-url
repeat: no-repeat (not necessary, cuz u wanna use only 1 big image)
position: fixed (this means your background stays in place when you scroll)

background-size:contain; (automatically fits the size of your image to the size of the page)
margin: 0 auto;