Trac: Nav links are misplaced and invisible

[SergeyBiryukov]

Background: #4513

Reported by @joyously in ​#meta on Slack.

[8916] caused Trac nav menus to be misplaced and displayed in white color on white background, making them invisible until you manually highlight the links. See the screenshots of the current and previous appearance.

At the moment, it's a bit tricky to reproduce, because the version of wp4.css is bumped differently on Trac vs. the rest of WordPress.org, causing different versions to be cached.

​https://wordpress.org/news/ currently uses version 80:

<link rel="stylesheet" href="//s.w.org/style/wp4.css?80" />

Trac still uses an older revision:

<link rel="stylesheet" href="https://s.w.org/style/wp4.css?78" />

Steps to reproduce

1. Open any Trac ticket page, e.g. #4513.
2. In browser's dev tools, replace wp4.css?78 with wp4.css?80 to load the latest version. Or, just remove float: left; from #headline h2, like [8916] did.
3. Notice the nav menu ("Handbook", "Blog", "Projects" links) disappear.

Suggested resolution:

• Either replicate [dotorg15156] (adding float: left; to #headline h2) on Trac, or restore that removed piece globally in wp4.css, after making sure it doesn't reintroduce the issue [8916] was trying to solve.

cc @coffee2code

[coffee2code]

In 9058:

Trac: Fix display of subheader links after recent changes to wp4.css.

Prevents links from displaying outside of subheader and being white text on white background.

Props joyously, SergeyBiryukov, coffee2code.
See [8916].
Fixes #4612.