@murray644,
The entire widget is wrapped in a class that is defined within the Widget settings – by default it is ‘search’.
This class currently has now CSS assigned to it in your theme so you have 2 options, 1/ create some CSS for that class or 2/ find another class name that is defined as you’d like already and change the class name in the widget to that.
From what I can see of your CSS the sidebar class will do part of it by will need some further tinkering to complete your changes.