How implemented: make a screen of different sizes for display?

Question

PHP

Hello. Guys, tell me how such a thing is implemented?
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It adjusts screen sizes (mobile, tablets, PC) thereby helping to view pages in different resolutions.
How can I do the same? Most likely there is already a ready-made such thing!
I just don't know how to google it properly. And generally do!

Answer 1

$("button#mobile").click(function(){
   $("iframe#mobile").css("width", "480px").css("height", "800px");
});

More or less like this.

Answer 2

Media Queries