What's the fastest way to learn coding as a designer (with an old-school programming background)?

I'm a designer who has a basic HTML & CSS skill.

20 years ago, I learned to code PHP & MySQL by myself. I created a simple chat program, web board, login&member system... all was the history.

Today, I focus on Designing things (UX/UI) but deep inside, I still want to write some lines of code to create something by myself.

As you guys know, the programming world today is different and it's not so easy for a designer like me to deploy something as yesterday.

My question is, how can I get back to the coding world again?