My site theme-editor.php seems broken

I’d like to edit my site’s default blog post template, but I can’t seem to figure out how to even view the template.

When I click the Theme Editor option within WordPress, it loads style.css by default. On the right sidebar of that page is a list of other .css and .php files, some of them appear as hyperlinked files (blue text).

Problem #1:
None of those hyperlinks can be clicked

Problem #2:
The list is longer than what appears on the page, but it will not allow me to scroll down to view the rest of the list. I can even see the top of the text of an item just off the screen, but I cannot scroll to view it.

The page is basically broken. Any idea what might cause this?

Here’s a screen cap of the page: https://i.imgur.com/zYyMxNO.png