Fix font size on thread summary.

Also fixes a few posts that generate odd HTML.
Merge branch 'thread-summary-font-size'
Fix colours on thread summary.
Merge branch 'dark-thread-summary'
Fix background colour incorrectly applying to popup.
Merge branch 'dark-popup-regression'
Fix light headers on login popup.
Merge branch 'dark-login'
Also apply to HTTPS pages.
Merge branch 'domain-rule'