CSS-blocks.com is the closest high-quality tool like this, but it's approach is slightly different, it doesn't work against any page, but for this approach it's

CSS-blocks.com is the closest high-quality tool like this, but it's approach is slightly different, it doesn't work against any page, but for this approach it's by far the best quality and most powerful tool like this right now. And, it's made by one of the maintainers of Sass