I made a number of formatting changes to several basic pages using a Bootstrap-based premium theme. The changes accomplished what I wanted but I subsequently noticed that, when I visited the site as an anonymous user, the top roughly 1/2 inch of the content part of each page is not displayed. It's as if the top of the page is hidden behind the horizontal menu bar at the top of the page rather than appearing correctly a 1/2 inch down.

I backed out all the changes I could remember making but it's still broken. It displays correctly when logged in as either admin or an authenticated user. I don't know how to even begin troubleshooting this issue. Can anyone point me in the right direction?