It depends on what you mean by “learn”. You can get a good grasp on it in six months. It can take years to truly “learn” it.
As I learn more and more, each thing I build is better and better.
I don’t know where you are on your path, but I might suggest that there are plenty of tricks left for HTML and CSS to teach you. Especially CSS - I’m always amazed how many new things I keep learning about CSS and what it can do.
Just keep learning. This is a lifelong pursuit.