"modern environments" meaning if you're shipping un-transpiled code, this will work on 93% of browsers. See full compatibility at caniuse.com/…

This approach also splits email development for modern email clients and older clients in two. You can use Safari/Chrome to test and develop modern techniques for WebKit-supported clients while using Firefox for your baseline experience for older clients like Outlook.

This media query only targets WebKit-supported email clients—which have incredible support for HTML5 and CSS3. This media query allows you to use of modern techniques like HTML5 video, CSS3 animation, web fonts, and more.

Microbundle also outputs a modern bundle specially designed to work in all modern browsers. This bundle preserves most modern JS features when compiling your code, but ensures the result runs in 90% of web browsers without needing to be transpiled. Specifically, it uses preset-modules to target the set of browsers that support <script type="module"> - that allows syntax like async/await, tagged templates, arrow functions, destructured and rest parameters, etc. The result is generally smaller and faster to execute than the esm bundle