Add some mobile-first styling

Some of the changes here include:

  * Adding a reset.css for good control of all styling

  * Using only the center portion of the window for a very wide window

  * Dropping wasteful margins around page content for a narrow window

  * Forcing input fields onto their own rows

  * Use grid display for form for consistent input width

  * Use 2-column for on wide windows and single-column for narrow

  * Use more modern flat styling for the submit button

  * Drop the ugly dashed outline for button focus