Download and extract to ModOrganizer\stylesheets\ folder
Known Issues
Links are hard to read on dark background. Unfortunately it's impossible to fix through styles. But you can lighten background color (e.g. QWidget { background-color: #8B8C93; })
Transparent background on hover for disabled check box in the Archives tab. Can't figure out how to fix it (if you care)
If filter is applied fancy border disappears. Also there is so no red border around mod list. I cannot fix it because it's hardcoded in MO source code. Optionally I can remove image border.