I would be easy to give you a lot of references to things you could go and read, but the real question is what do you want to archive? Programming is only a means to an end, and you can do everything with the tools you already know such as PHP, HTML & CSS.

React.js or the meta-level behind it, virtual DOM, has no doubt improved my front-end skills 10-fold and together with Node.js where I can render all the things in the backend and use the same code, but all that doesn't really matter.

What are you doing currently? Maybe I can help you get started? What are your interests?