Is there a way to get a youtube video to expand when you press play using CSS?

Simple as the title, I’m doing a university project. I have coded a piece which has a video embedded into it, the thumbnail appears where I want it too, it’s small but that’s fine.

However when I press play, the video stays the same size and you can’t really see it, is there anyway to get the video to expand upon pressing play?

Any advice or help would be good! FetLife

I have not heard about this before but it looks interesting. I always make programme through plugins and the plugins are to be attached with the HTML coding and CSS designs. Now, I am using the plugins UAE and hope that it will be useful in your case.