Firefox Developer Edition has visual tools for transition functions, font tooling, flexbox, grid, clipping and pretty much every CSS nuance. It's also available

Firefox Developer Edition has visual tools for transition functions, font tooling, flexbox, grid, clipping and pretty much every CSS nuance. It's also available for free and always will be, is decoupled from your source code (while still providing you with visually-edited code if you want to make a change permanent) and is built into a browser.