Zenlite image display width

I just switched to Zenlite theme and I think it’s even more satisfying to my needs than Pilcrow (much as I do love pilcrow!!). Fingers crossed, no problems yet! It even appears to be handling my wide images and banners fine. I am curious, though, about the exact dimensions allowed for display width. Can someone advise where in the files I would find out? I realize not all themes put their info in the same places… And again, I know very little about css.