Apple has released Safari Technology Preview 199. The update includes includes bug fixes and performance improvements for Web Inspector, CSS, Rendering, JavaScript, WebCodecs, Web API, Media, Web Animations, HTML, Accessibility, Security, Privacy, and Safari Web Extensions.
Safari Technology Preview offers a sneak peek at upcoming web technologies in macOS and iOS. You can experiment with these technologies in your websites and extensions. Safari Technology Preview is a standalone app that works side-by-side with the current version of Safari, so you can continue to use and reference the current release.