A minimal library which polyfills the ResizeObserver API and is entirely based on the latest Draft Specification.

certainlyakey starred javan/details-element-polyfill

Polyfill for the HTML dialog element

Target elements if they are focused or contain a focused element with a PostCSS plugin and Javascript script

Polyfill for CSS position: sticky

A ponyfill that provides client-side support for CSS custom properties (aka "CSS variables") in legacy browsers

Polyfill for native IntersectionObserver API

Automatically adds datepickers to input[type=date] on IE, Firefox, and OS X Safari.

PostCSS plugin that updates the standard object-fit tag to work with the object-fit-images polyfill for browsers that do not natively support object-fit.

JavaScript polyfill for client-side hyphenation

certainlyakey starred inexorabletash/polyfill

This polyfill makes it possible to use attr() like it is defined in the spec.

SVG for Everybody adds external spritemaps support to otherwise SVG-capable browsers.

A proof-of-concept event-based CSS element dimension query with valid CSS selector syntax.

So here we're collecting all the shims, fallbacks, and polyfills in order to implant html5 functionality in browsers that don't natively support them.

Look up HTML5, CSS3, etc features, know if they are ready for use, and if so find out how you should use them – with polyfills, fallbacks or as they are.

A polyfill, or polyfiller, is a piece of code (or plugin) that provides the technology that you, the developer, expect the browser to provide natively. Flattening the API landscape if you will.