How to change the width of the mantra theme page?

I am using the recent version of mantra by cryout creations version Version 1.9.9.6 and I am having trouble editing the overall width. I want to make it slimmer. I have looked in the styles page and main theme page to edit the wrapper, but have edited with no luck. The option they have built in only edits the size of the side bar and content individually, not the whole width of the page. Do I need to edit multiple sections, like header, content, etc, or is there a wrapper type code that I can edit for all? If anyone can point me in the right direction I’d appreciate it, thank you.