How do I modify sidebar widget appearance

Hi,

I’m trying to use the GD > Search widget in my main sidebar. I would like to be able to manage the format but cannot find where this is done… I only have one minor issue right now, the size of the search button (see attached file)…. but I’m not just interested in modifying that… was hoping that if I understand where to modify that (ie css? or is there a “control panel”) that it might provide me with some other options.

Apologies if this is obvious… I’m new to both WordPress and GD.

thanks for any help.
darren

WordPress 4.3
Theme: MultiNews (2.2) Child (1.0)
GeoDirectory: 1.5.1
GeoDirectory Multinews Theme Compatibility Plugin V 1.01