It works great on MP6 2.1 now. Though, alignment issue is still there (theme name and buttons are not in line with option names inside accordion) and lots of new bugs have appeared:
- color picker alignment on select.
- dark, semi-transparent RGBA border or no border around buttons would be better, now buttons appear blurry.
Issues outside Customizer:
- You should be able to drop widgets into closed sidebar (sidebar should open on-hover and close back on-hover-out if it is closed by default)
- Inactive widgets options are not styled correctly.
- Input field border color should be #bbb or #ccc to make it sharper, unified for all fields across admin (checkbox, select, option, textarea, ...).
- Menu alerts should be square, not circle. Rounded corners should only be added to buttons and even that is questionable.
- Top menu icons are totally out of line, whereas left menu icons are perfect. On mobile, it's even worse. It just doesn't feel right.
There are other UI issues, but I'm not sure if this is the place to post them?