HTML and CSS Web Designing

Where can I learn professional web designing on the internet?

Don’t exactly know what you mean by “professional”.
But Reference manual/documentation for HTML and CSS are all over the web.

The trick is not having head-knowledge of these individual HTML/CSS, but actual hands-on PRACTICE so you’ll know how to combine them. And the only way to do that is by lots of work, spending lots of time on your own projects.