Styling up Jump Nav text box

Summary:
This actually gives it a smooth look across all OS and browsers. Copy-paste from form inputs.

Motivation (aka Disclaimer)

I felt kind of... disturbed that it looked different in every browser / OS combination I have at my disposal. The range is from ugly (Chrome on Ubuntu) to pretty (IE9 on Win7 ¬.¬). I give a few examples

• Ubuntu
  • Firefox
    • Actually looking very nice. Rounded borders and orange border on focus are default from UA style sheet?
  • Chrome
    • Looks ugly. 2px inset mid-grey border. What you would expect from Win '95
    • 1px inset mid-grey border (Win '98 style) + orange webkit outline.
• Windows
  • IE9
    • Nice blocky text input with black border. Blue border upon hover. Really black border on focus?
  • IE10
    • Kind of same as IE9, though I had the feeling that it had a deeper black border
  • Firefox
    • Looks so normal that it is actually boring
  • Chrome
    • Looks pretty much normal, until focus where you get the webkit outlines. Ugly

No Mac, since I have no Mac. Also no iPhone/iPad. Have Android 4.1/WP8, though I never visited Phabricator with them

Test Plan:
Looked at it in

• Ubuntu
  • Mozilla Firefox
  • Google Chrome
• Windows 7/8
  • IE 9/10
  • Opera (Opera?)
  • Mozilla Firefox
  • Google Chrome

Everything smooth (exceptions in case of no border-radius/box-shadow)

Reviewers: epriestley, btrahan, chad

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5515