How to widen general 'content' area of posts (along with header)?

[jforman]

I love the Blowfish theme for its simplicity and included features, but I'm unable to figure out how to apply a wider width to the content (and header) areas of my website.

How do I widen the main content area for posts (the blue area on the below screenshot)? I've got a 4K monitor at home and the content is quite narrow, causing a TON of line breaks:

I've read up on https://tailwindcss.com/docs/width, to try and implement something like w-4/5 for my content with the remaining with split on each side, but I'm not sure HOW to do this. I just want to change that one parameter.

Any guidance is greatly appreciated.