inline editor and image holder changes

I made a couple of changes as I was unable to read some of the code in an inline editor due to the very light background.  The core team has made a default styling for inline editors if `dark: true` is specified.  Unless you want to get into a bunch of changes with many little styles, it seems best to just rely on the default styling for your inline editors.

Also, changed `#image-holder` so that the image viewer (which doesn't have default styling from core yet) reflects your theme colors.