how to stretch a site across the entire screen?

[ Moderator note: moved to How-to and Troubleshooting. ]

I have a hard topic: BlaskHosting, only two columns: the center and the left sidebar. one file CSS is displayed in the console settings threads other three files CSS are in the folder :www\wp-content\themes\BlackHosting\css. As a result, two files style.css and screnn.css are responsible for the size of the site, but I did not get it right stretch the entire width or even just to increase the width of the site. Taught but does not go 🙁 I hope someone can help. Thanks