Elements Not Centered

Ok, so this is probably a rather simple problem… but I need some help please. I recently bought a new laptop with a 17″ monitor and realized that when the screen is enlarged (I had a 15″ before), my blog does not center itself in the browser.

My blog is here:
https://peatbog.net

My stylesheet is here:
https://peatbog.net/wp-content/themes/Green/style.css

Can someone please tell me what needs to be changed so that the contents are centered in the middle of the page? I tried changing the main elements to “relative” instead of “absolute” as they are now, but that didn’t do it like I thought it would. Please help.