On the developer tool you can modify CSS on the fly and the display changes instantly.
But if you click view page source you will get the original css of the document
It could be wonderful to have an that CSS by a command or a addon.
Edits that you make in the Rules view are reflected in the Style Editor, and vice versa.
To open the Style Editor choose the "Style Editor" option from the "Web Developer" menu (which is a submenu in the "Tools" menu on the Mac). The Toolbox will appear at the bottom of the browser window, with the Style Editor activated:
Upon an external style sheet rule modification, the respective resource text is updated in the Resources panel, and the revision history is stored for such style sheet resources until the DevTools window is closed.
Activate the Resources panel, find tutorial.css in the resource tree. Note that the tree node is expandable. Click the arrow next to the node title, and you will see all the resource modifications that you have made above.
Select any revision to see its differences from the original stylesheet resource, highlighted line-wise.
You can drag and drop a stylesheet revision node into most text editors to export the revision content.
Source Editing styles