I've used plenty of CSS editors, mostly browser extensions. They were great for getting me through, and seeing instant changes.
Then I upgraded to Sizzy. Sizzy is an absolute beast of a browser, covering multiple simultaneous viewport sizes, great debuging features, and a whole bunch of developer-centric features, most of which I don't use. It's massive overkill, though, for someone building websites with a pagebuilder, who just needs to make sure everything is running smoothly, or to find out where that pesky padding is coming from.
InTab walks the line between that collection of tools you've hobbled together for free, (without realising how much time you waste doing so) and expensive tools like Sizzy VERY well.
There are a few bugs; screenshots don't seem to take the full page (shearing off below the fold into white) and some sites don't respect the viewport settings ( google doesn't resize properly on InTab, but does on Sizzy) but I imagine these will become problems of the past, as the developer seems very active on Trello, and has a well considered roadmap.
Normally I'd wait a while longer to write a review (I've been playing with this for less than an hour) but InTab has already far surpassed my usual tools either in increased features, or cleaner UI.
InTab will be my CSS editor of choice for 90% of the time. No question.
Hats of to the dev! You've got some great software here!