When I\'m working with CSS, I\'ll often test in a browser - say, Chrome - right click an element, click Inspect Element, and edit the CSS right there. The use of arrow keys
I built a Chrome extension that does exactly this.
It's called StyleURL - it takes whatever CSS changes you made in Chrome Inspector and outputs valid CSS as the diff: https://chrome.google.com/webstore/detail/styleurl/emplcligcppnlalfjknjbanolhlnkmgp
Here's an example where I added "padding-bottom: 50px" to this page:
It's open-source and on GitHub too: https://github.com/Jarred-Sumner/styleurl-extension
In Chrome there is also the Changes tab in the console drawer that displays all the modifications of CSS. It's not an export, but at least it is very convenient to quickly grasp what has changed.