A good approach, and is what I did to learn, is thinking of what you want to make, i.e a simple home page. Then find a page you like the look of and use the "inspector" element on your browser by right clicking > inspect. This is a good way to see how pages are built and how CSS classes work with them.
When you get stuck trying to make something, I recommend using w3. If you're having a hard time thinking of a project or getting started in general, I would recommend code academy free courses, The Odin project or just looking up videos on youtube.
Edit: I would recommend changing your background to something else, that could seriously trigger someone's epilepsy.