where is css code for column width?

Hello- a question in several parts- buddymatic theme, my site is https://www.informalchemy.com I’m new!
I’m trying to widen the main column on SOME of my pages: specifically the home page and each of the ‘project’ pages. I’m having trouble finding the code lines that edit the column widths. My background is white, so I’m under the impression there is no .jpg in the right column overlaying my widened left (or main?) column- but I’m not sure. In my styles folder, I have css files titled 18px, 21px, adminbar, buddypress, classic, default, images, plugins, reset, and typography. In ‘buddypress’ I’ve tried altering the pixel width in lines 120, 124, and 143 but nothing changes on the site. I’ve successfully edited/re loaded the typography and default files to make other changes to the site so I’m reasonably sure my ftp is working properly. Is ‘buddypress’ the proper file to edit? thanks for your time… very much appreciated.