Option to Center Iframe on Page

[EnigmaSolved]

I am using this extension to load a page that contains a large image. It would look nicer if there were a setting to center the iframe on the page, instead of it being left aligned as it currently is. I've played around a little with editing the html/css in Inspector, but haven't figured out the right code/syntax for achieving this (the usual methods I have found don't seem to work for some reason). And, of course, even if I get that working I'd then have to get another extension that would let me inject that code into just this New Tab page. It would be awesome to have this as a built-in setting (ie, "Center Iframe on Page").

Thanks for your consideration!
:)