Omnipay is a payment processing library for PHP. It has a clear and consistent API, is fully unit tested, and even comes with an example application to get you started.

Online and visually :nth css tester made by CSSTricks.

Stylemug is a fast css-in-js library that extracts atomic CSS rules to a .css file. It generates atomic CSS from the static stylesheets defined in JS. The compiled rules are extracted to a .css file.The stylesheet code in the Javascript bundle is replaced (no CSS in JS) with a hash map for classnames lookup at runtime.