What js library do you recommend for popups?

Question

CMS

It is necessary to make a button that will hang on the side of the page and expand into a pop-up window on click, in which you can display information about discounts and an offer to subscribe to the site's newsletter.
Probably, this has already been implemented in some js library, in which it is enough to style the button a little and make your content in a pop-up window. Please tell me if you know.
You can, of course, also write something of your own in a quick way, but there will certainly be problems with cross-browser compatibility and the like.
You have definitely seen examples of this - these are jivo or livetex online consulting services, or feedback like reformal.
Upd. Found about what I was looking for feedback-me.appspot.com/example_clean.html
But a) this is a plugin for jquery, I want something without dependencies, more compact, b) it looks a little poor out of the box, I want a beautiful, sexy look
Upd 2. For those who are interested. Found another good example. pupunzi.com/mb.components/mb.extruder/demo/demo.html - especially the tab on the left draws attention well.

Answer 1

fancyapps.com/fancybox

Answer 2

Here is a good selection of pop-ups
In particular Kendo UI/window

Answer 3

fancybox only! Nothing else is needed! Customize as you want, loads whatever you want.

Answer 4

dimsemenov.com/plugins/magnific-popup - great stuff and free license

Answer 5

native js

Answer 6

https://fancyapps.com/fancybox/3/