Hello Yahoo,
This New Mail layout sucks. It is really bad. It is the worst. I cannot think about any way it can be worse, but probably your engineers and UI/UX people (who cannot find a job anywhere else) can still figure out a way.
The old layout was very good. Instead of making improvements to that, the not smart people of Yahoo made it the worst.

1) There is no option to change the color scheme.
2) There is no option to change message spacing. On Compact setting, there is still a lot of empty space
3) Hitting Esc key on keyboard does not close a message or tab.
4) Search icon on the message line is moved to the left instead of its better position on the right.

I hope someone is wise enough on Yahoo Mail to give an option to revert to old/classic layout.