For fifteen years, every modal, dropdown menu, tooltip and accordion on the web came from JavaScript libraries that fought z-index wars, trapped focus by hand and often forgot the Escape key. HTML now ships those behaviors as markup. A <dialog> knows how to be modal, a popover closes when you click elsewhere, a <details> group keeps only one panel open, and a <button> can open any of them without a line of script.
The native versions get keyboard handling, focus management and accessibility roles for free, and work before your JavaScript loads. Each subsection states the feature's Baseline status (see The Living Standard); "newly available" features work only in current browsers, so check your analytics before dropping a fallback. Popover and Dialog in JS drives dialogs and popovers from JavaScript.