You should be able to learn enough of the basics of HTML and CSS to allow you to build a simple web site in a couple of hours. I suggest learning it by watching a video of someone live coding a website and explaining each line as they write it.

Focus on learning big picture concepts – in this case what HTML tags and CSS Selectors are – and don’t get too caught up in memorizing all the specific tags or syntax. You can always learn that stuff as specific cases come up.

Later down the line if you don’t know how to do something you can always do a Google Search to figure out how to do something. You’ll see a ton of articles explaining exactly how to do that. That means that you should focus on getting proficient enough with HTML to be able to understand those types of pages and be able to learn the specifics on the fly.

I suggest avoiding doing in-browser stuff, like Codecademy, simply because learning by writing code and seeing the result as you code it will help you learn the material much quicker. You can follow-up my simple tutorial on Start from Scratch for HTML & CSS also. I tried to keep simple & basic, so that you can experiment with it on your offline computer also.