After some tweaking, I managed to get the search bar to play nicely. I unrounded the corners and lightened the borders to match the framing lines elsewhere in the navigation bar. Here is the CSS for it. You’ll want to give it an id selector of your own, a la #searchform.
Here is the CSS for the changes to the search bar.
In trying to embed the above gist, I noticed that octopress breaks the styling:
Now I have something else to work on.