With Progressive enhancement, you make sure that everyone can access your site or app. You do this by making sure the information or functionality is available in the simplest of technologies (often just HTML) and testing for support for additional features and complexity before adding them.
For example, a form should work with just the HTML available, but could submit without a page refresh using JavaScript if that is available. You can also use a progressive enhancement approach for design by making sure the site works on all browsers, but adding additional non-vital CSS effects (like backdrop-filter) to make the site more visually appealing in browsers that support it.
