After moving the indicator dot away from the default bluish/purplish color position and then moving it back the tone is wrong (bright blue).
The real default tone is located somewhere almost at the bottom while moving the dot manually. But in this case the color of the tabstrip is not the same (gray) as in the default position.

*Yes, it still possible to hit the default position manually if being very precise and in this case the theme's default tone switches on instantly despite of the bright blue palette's area.

we are considering hiding that horizontal tab strip

the empty tab strip is a good place to clearly show page name in the center while in vertical mode. Hiding should be optional, not by default.

The vertical tab strip is currently resizeable you can make it as small as the fav icon of the opened pages

I noticed that the start page favicon gets cut off a tiny bit when you shrink the vertical tab strip all the way.

• I guess the vertical tabs panel shouldn't be as high as the pinned sidebar (should be below the toolbar/bookmarks bar).

*Btw, it possible to achieve such layout by turning on 'autohide sidebar'.

• the vertical tabs pane should have pin/unpin option like in Edge. So when unpinned the narrow bar will be only shown (only favicons), on hover the pane will expand.

• expanded pane could contain search tabs field and recently closed dropdown button (like in Edge as well).
  

*Pls, fix the 'redesigned' search popup. it's not usable in current view.

Vertical Tabs is now available

Maybe I'm wrong, but it seems like a copy paste of the recently introduced vertical tabs in Chrome.
https://blog.google/products-and-platforms/products/chrome/new-chrome-productivity-features/