you tried adding a widget with adding css
basically css is for 'styling' and widgets are 'function/content'
see they are different by nature?
Atahualpa is loaded with options .. more than about any other theme.
but that makes that this theme requires you to do some studying.
Most is already explained very well right inside the theme.
In other words .. most info is laid out there already, clearly explained, even accompanied with lots of examples .. but its up to us .. the users .. to do some legwork and read whats already explained right inside the theme.
In this case .. have a look at the 'Add new widgets AREAS' section ..
judging by the title, I suspect it might
explain what you are looking for.