Using Feature Queries in CSS

For years, developers have used Modernizr to do what Feature Queries do — but Modernizr requires JavaScript. While the scripts might be tiny, CSS architected with Modernizr requires the JavaScript file to download, to execute, and to complete before the CSS is applied. Involving JavaScript will always be slower than only using CSS.

An exhaustive article by Jen Simmons on how the feature query @supports work in CSS.