Adjusted margins and font sizes to better match the input box specs

[Blackbaud-PaulCrowder]

No description provided.

[codecov]

Codecov Report

Merging #127 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #127   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           29        29           
  Lines          951       951           
  Branches       127       127           
=========================================
  Hits           951       951           

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[blackbaud-ado]

Preview build at https://host.nxt.blackbaud.com/skyux-forms?_sp.spa=pr-input-box-sizing-fixes