The search field is too wide, causing the Search button to overlap with the site icons in the Hot Network Questions list.
The tag description box seems to extend too far to the left, or the text above it is positioned too far to the right.
This might possibly be related to my choice to hide the left sidebar across the network; I haven't actually tried this with the sidebar visible.
The above is with Firefox ESR 60.2.1 on 64-bit Debian GNU/Linux. The black part to the right of the URL bar isn't actually black; I just blacked out my browser extensions' toolbar buttons.
Yes, that's a real search; I was trying to see if Missing whitespace in beta site statistics box had already been reported.