An extension for Google Chrome to add custom CSS on websites.

Secure. The extension does not require permissions to access all data on all websites all the time. Once you start editing CSS on a page, you get a permission prompt specific to that domain.

Later, if the CSS for a domain is not used, the permission will be dropped.

Minimal. There are no UI clutter of any kind. The entire extension consists of a big editable area for CSS code for the current domain.