Ned, Mark will be opening several appearance issues (see ttk thread on Idle list).  Do you want to be routinely added as nosy to comment?

Mark: The description and labeling of the screenshot is a bit off. For Windows, the full window is inactive ([ x ] is not red). The Linux and Windows inset labels are reversed (and the Windows one inactive).

1. I added the ttk import and prefix to EditorWindow and hit F5 to test. The result matches what appears to be the native Win7 scrollbar.  I am ready change all the scrollbars.  Lets make this a separate first patch.

2. The current Tk/Toplevel frame appears to be the native frame, at least on Win7. So I do not see anything to be done away with to match the platform.  The semi-transparent frame gets grayer (less transparent) when active.  There is additional darkening along the bottom and up 3/4 the sides.  I do not care about Win8 as, judging from Stackoverflow, it seems to be less common among Idle users. I expect Win 10 will eventually be a different matter.  I will eventually upgrade after I get the notice.

3. I agree with deleting the sinks: useless and ugly. I do not believe anything else has a status bar.

There is much wasted space.  Notepad++ has file type, length (chars), lines, lineno, colno, selection length, "Dos/Windows"??, "ANSI"??, and  Ins(ert versus Overwrite on insert - not available with Idle). I am not sure what would be useful, but adding stuff would be a separate issue.

4. Windows bar looks fine to me.  Light gray, same active or not. For me, the font, the same as on the menu, is already small. No smaller. In fact, I have wondered whether it would be possible for users to adjust the size of the 'other' fonts also.

5. Ned's territory.