Customize the web by adding your own js and css to websites.An extension that lets you add per-domain custom CSS and JavaScript that will be automatically applied/run on every page of that domain.
This works a lot like dotjs, if you know what that is, except there are no files and no server daemon. All data is stored on your chrome local storage (*not* HTML5 localStorage).
**Note**: Data is *not* synced across your systems due to very limiting quota limitations imposed by Chrome extension API.
Although I've been using this extension myself for quite some time, I'd still consider it beta. I advice you to regularly take backups of your data and save them.
And no, you can't trust me. The extension is open source (MIT License). If you are paranoid like me, you may check the source code at https://github.com/sharat87/custom-web.