Here is the complete list of tools I use when I design in the browser using css and html.
I try to write as little css as possible at this point. Tachyons is normally my base for putting something together. It handles most of what I need, is easy for me to extend and weighs less than 11kb.
For processing and manipulating CSS files.
I use the following modules:
For auto-updating the browser after changing code.
For managing build flow and dependencies.
A Web Browser
For visual testing my css is working. I normally test on lynx, safari, chrome, and firefox.
For writing HTML/CSS.
For visualizing various stats about the css I'm writing.
Pen & Paper
I still use pen & to write down notes and sketch out design ideas. When I'm building a complex component I generally write down a list of things I know about the component and a list of things I don't know for sure.