Retention! I keep drawing blanks when I try to start a new Project

Hey, guys! I have officially completed all of the course material bar the certs for HTML/CSS. I was like awesome! Now to practice! So I went over to to do one of the challenges. I was gonna make a marble that rolled along and paused at the top of hills while reflecting sunlight etc. Point being I knew what I wanted to make, I could see it clearly, but I couldn’t remember any of the CSS I need to do. I stared at a basically blank screen for forever. I have no issue doing any of the course material though. So my question is do you all have any tips for remembering elements?

Don’t try to memorize. Google. Look things up.

I understand that there are way too many to memorize them all, I just…I feel almost like I didn’t learn a thing, you know?