How do I switch back to the previous user interface style

Is it possible to restore the v31 pre user interface style? Why the user interface has been changed in the first place? The user interface was the area with the least amount of questions, especially when it comes to style and colors. I'd rather see Mozilla devs allowing multiple clients sharing the same locally stored in structure of the mailbox that waste their time on evolving user interface.
So, is it possible to get back to how it looked like before rather than having everything be gray and dark blue battleship? It's especially annoying when creating new emails. The header section is all gray offering much less contrast and with weak lines, there is barely any spacing between header lines. It is totally against what produced the 30 years of UX research.
A cure for this?

Themes of the addon:

If you really want o back to the 24.6.0 version:

Tags: Thunderbird

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