Quick markup and CSS consolidation for search
Set font size in px on html tag

The trick used here was designed to honor the font setting in a user's
browser by assuming a typical default of 16px and computing the base
font size in ems relative to that.

The problem is that even if everything is sized in ems there are
sometimes aggressive user agent styles that complicate things by
restoring the system font. It turns out it fixes the various things
I've noticed in my FF this way.
Kill the px calculations in the search styles

Besides the line height hack for FF kill the rest of the px related
calculation and do everything in nice, pretty ems.
Enforce a consistent line height in the top bar
Merge pull request #1364 from hypothesis/simplified-search-css-html-tweaks

Tweak the HTML and CSS of the new search input.