Themes not working properly PC/Android

So I've been thinkering with themes this weekend, and modified it to my likings. The backgrounds are problematic however, but I've made it so it scales very good on my PC, using Chrome.

But on my phone it doesn't scale very well, and there seems to be doing something differently on the comic-rootlink page, and when going into the folder itself -with the background. And that's not something I can really do anything about as the comics.css is covering the whole thing.

My background is set in body{} only and it scales and looks perfect on my PC using Chrome. But even the homepage is changed from PC to Android both using Chrome. When using Firefox on my phone the homepage looks like it does on my PC, but then it looks slightly differently when logging in. But it doesn't change the background from rootlink page to the actual listings, like in Chrome.

This is pretty frustrating, and I can see now why there's not a lot of themes out there for the people to download.