- Select from the list of style sheets included into the web page.
- Select which properties from which rules you wish to edit.
- Edit selected property values, seeing the results immediately in the web page.
- Save any changed values as CSS source code, which you can cut and paste to update your CSS source files.
You can try it out at http://pdorrell.github.io/style-adjuster/.
Style Adjuster is available as a Google Chrome browser extension at https://chrome.google.com/webstore/detail/style-adjuster/bmnmiidhocohelghddfcfbhojknfclba.