Here's a quick interface I built just now:

There are several customizations OUTSIDE using MGB.

1. File Icons: Unzip and put the individual files in your moi/ui/icons folder. They don't replace any others there as the originals are stored as a resource in the app.
https://altuit.cloud/web/dbpub/MoIGUIdownloads/MoiFileIcons.zip

2.MainWindowCornerSizer.png* Only for Mac (I think). Icon for resizing the window (look at bottom right of image). Put in moi/ui folder (don't forget to back up old version!).
https://altuit.cloud/web/dbpub/MoIGUIdownloads/MainWindowCornerSizer.png

3.ViewportForeground.png* Creates a darkened bar between viewports. Put in moi/ui folder (don't forget to back up old version!).
https://altuit.cloud/web/dbpub/MoIGUIdownloads/ViewportForeground.png

Also, you'll need to use the Options View and Grid property panes inside of MoI to set the background color and the grid.

Here's the template for loading into MGB: (right-click link to download)
https://altuit.cloud/web/dbpub/MoIGUIdownloads/darkInterface.txt