TPAC: Consolidate and simplify button styles

TPAC: Consolidate and simplify button styles

TPAC has at least two distinct types of buttons, those created by
input tags, and those created by anchor (that is, <a>) tags.  This
commit simplifies and consolidates the styles used for both types
of buttons.

Also, inputs do not inherit the body font by default, so let's apply
it for better display consistency.

Finally, Firefox inputs have some extra space around them; let's make
a modest attempt to remove that.

Signed-off-by: Dan Wells <dbw2@calvin.edu>