Insert custom CSS into pages, immediately see the visual results, and have that CSS persist for future visits.
You may dislike a given site's design and want to add your own touch--that is, your own style--to make it aesthetically pleasing. After installing the extension, visit the site (e.g. techcrunch.com) and hit control + m. You should see a textarea to the right of the browser window. Insert your custom CSS into it and view the results.
This CSS will be reinserted upon revisiting the site, thereby saving your styles. Pressing control + m once more will hide the textarea, but your contents will still be retained.
See <https://github.com/karthikv/my-style> (scroll down) for an example.
To speed up the process of styling, if you hold alt while clicking an element, a selector for that element will automatically be appended to the textarea editor. With this, you can circumvent the time it takes to inspect the element to find how to target it.
How it Works:
My Style is quite simple. It inserts a textarea into the page, looks for changes to the textarea's contents, and updates a dynamically inserted style tag appropriately. My Style employs local storage to make CSS changes persistent. It uses simple technologies for a simple result.