Header decal problem and resolutions problem, help please

[Goodman_2020]

Hello
I tried to begin the creation of my own header but theres a problem. No matter what size i try i've got a decal (sometimes on the right, sometimes o nthe left, sometimes big, sometimes thin...but always a decal, no matter the size exactly what i need). So i would like to know how to do to make my header doesn't have this decal anymore and is perefectly fixed to the forum. I know it's possible because once on a forum i saw how to do it, but i don't remember where.



Second problem, when i reduce the window i got something horrible with the header see by youself



How to do to make it doesn't move (like on this website, when you reduce the window nothing happens to the forum)

And when i reduce to much the window i got the purple background appears under my custom background!

I can't imagining the mess it would be for me people using 1024x768 resolution or less

Is there a way to make all stay where it is and adapted to serveral resolutions (1280x1024;1024x768;1680x1050;1920x1200;1400x900;1 600x1200)

Thx!