Change Paragraph Content Width

Hey guys,
I’m trying to change the width of the paragraph text for Hamilton theme and I cannot find any information on how to do it. For some themes it should be available in the Layout options under Appearance but Hamilton doesn’t have this option.

Do you maybe know which CSS code could I use? I’m currently using the classic editor because I like the way it adds the gallery images, so I’m not planning to switch atm.

Thanks!