How is the style constraint set up?

Question

css

Sorry for the crooked title. In this template , the fields are very interestingly made. I pressed the field, the label moved up. I was able to implement it. But if I enter something in the field, the label will still return to its place and an overlay is obtained.

In the example at the link of this "artifact" is not. How can I fix this, where to dig? Is it at the css level or is it still on js (I deleted all js in principle and it still worked)?

Answer 1

I've tried in vain to do it in pure CSS, it didn't work. For me, you need to make different CSS classes with transitions, and then add and remove classes in JS