Two things:
- Please don't make the sidebar appear to be way bigger than the content actually inside it:
The way it is designed now makes it look like it is going to take up 33% of the screen, while the links only take up a portion of that apparent area. Combine that with the fact that it is stuck to the left edge of the questions area, and it gives the feeling of a super cramped view. As someone else said before, this is not 1990s Geocities. Move the sidebar to the left side of the viewport (sticky menus should be on the outer edge of the viewport, not the outer edge of the content).
At the very least, if you won't do that, let us collapse it to some icons and no text; like Makyen (and others) have said, we want to see Q&A. Stack Overflow is a Q&A site. All your other offerings and business models depend on users coming to SO for a quality Q&A experience. So take care of that first.
And I really can't stress this enough. Don't ignore chat
Chat does not resize correctly shows that chat is in a dire need of a responsive layout fix.