You have a combination of non-default settings at play. If you restore default colors and turn off “show tab text” for the panel tabs on the right, it will be consistent.
Yes, the intent is flatter UI.
The row of buttons on the properties panel has been my least favorite UI in Rhino for ages. But you didn’t even show the worst part:
Is that second “row” a set of buttons? Tabs? Yeah, it’s that awesome. We contemplated a second row of tabs; we contemplated forcing all Properties tabs into their own distinct group (ala Rhino for Mac). In the end, we didn’t come up with anything better than what we had before - just different.