Why is the search field so small?
Meta SO:
SO (aka old situation) for comparison:
Also I find it annoying that the menu isn't always in the screen anymore (while there is plenty of space).
Now you either have to scroll up or open the hamburger menu first:
It used to always be available on the top like this:
Collapsing the menu doesn't really give you more space. I would expect the main part of the screen would use the space of the menu when it is collapsed.