[Theme: Hatch] Post text area column width

http://darcysinclair.com/learnsixty/patanjalis-yoga-sutras/

I’d like to know how to alter the column width of the post text body block to equal the width of the image area.

Also, is there an organized way for a designer (non-programmer) to learn more about code and how to find and change? Good design can’t manifest without good code. I’d like to learn how to alter code. Suggestion?

Thanks!