Want to change Fluid width to Fixed px width in “veryplaintxt” theme

Hello, I wanted a very simple layout and found “veryplaintxt 2.3” and “Newspaper – 2a 1.0” in the theme viewer.

I like ‘veryplaintext’ better but I do not want fluid widths. I want to control theme width in pixels.

Is there a simple way to modify ‘veryplaintxt’ to easily control px width of content and sidebar, and margins, for a noob that is?

‘Newspaper’ is so easy to go in and change the fixed dimensions of content, sidebar, and their margins.

Any help would be greatly appreciated! Thank you!