Just like FireBug, this bookmarklet allows developers to load a/any Web page and update its native CSS code, seeing made changes in real-time.
Clicking the bookmarklet creates a small greyish editor in the bottom right corner of the page, where the CSS code can be added.
Clicking it again will make the editing box disappear.
All entered CSS code is stored via localStorage and is applied whenever the bookmarklet is re-opened. Also, they are URL-aware, so the code entered on one page will not be loaded on another.
Also comes with iPad/iPhone support.