Help with website setup?

I’m wanting to create a website with a specific design in mind. I want the page to have margins all equal medium sized (maybe 5-10%) and I want it to be fixed so as you scroll the page, the content moves down but the background is the same. Could somebody show me how to do this on a codepen possibly?

@tobiasmeyrick have you tried something like

body {
    background: url('yourbackground.jpg') no-repeat center center fixed;