What are adaptive modern sites and applications based on?

Question

css

I didn’t make up for several years, because. my main specialty is UI/UX design. Now I'm thinking of learning JS and brushing up my knowledge of HTML/CSS. In this regard, 2 questions:

1) On what typeset adaptive modern sites and applications, on flex, grids or something else?

2) Can someone tell me some life hacks on how to quickly refresh your memory in HTML/CSS. The knowledge is there, but I already forgot, I need some kind of quick course, video or book on the basics to refresh my memory.

Answer 1

1) What are adaptive modern sites and applications based on, flex, grids or something else?

Yes
Need an explanation?

2) Can someone tell me some life hacks on how to quickly refresh your memory in HTML/CSS. The knowledge is there, but I already forgot, I need some kind of quick course, video or book on the basics to refresh my memory.

If you spend time - then any course, video or book.
If you do it, then start doing it.