resize the "log in"/"log out" buttons

[srabraham]

It's kind of weird that they stretch across the entire screen. They also clash with the new nonprod warning banner at the top of the site.

This looks a bit more conventional now.

[github-actions[bot]]

⚠️ Optional matrix job Py:3.14.0-alpha.1 - ubuntu-latest failed ⚠️

• tox prefix: test
• exit status: 1