Unless you're using something else than a regular text editor/IDE for editing CSS, using UI controls to experiment with how things look would normally be faster for many. I'm a programmer myself, but having UI widgets I can drag or interact with is way faster than writing numbers and attributes, when it comes to coming up with a design.

Although, this assumes you're in the initial design phase of something, not the typical designer->developer handoff where you basically just want to implement a specification someone handed you.