Changed theme, now site is blank

Ok, I can’t seem to figure out how to undo what I’ve done. I selected to use a new theme on my site. Being the “smart” person that I am, I went to preview the new look of the site by opening the site in a new tab. The new tab opened up blank, so I went back to the dashboard in the other tab to try a different theme. However, when the screne refreshed after selecting a different theme, that page too opened up blank. Now, every single thing I click on under the blog directory opens up blank. The problem doesn’t exist in any other directory under my site, so it is localized to by /blog directory.

Is there any one file I can access within the /blog directory to “reset” the theme back to a default or force the admin page to load up? Or am I just screwed?

Site: https://uscommonsense.net/blog