Feature queries are a great way to progressively enhance your site and allow you to take advantage of the latest and greatest advancements in CSS, but only when it is supported in the browser. Feature queries are a way of adding an IF statement to your CSS in the same way that we do for media queries and viewports, but with actual supported features.
This article picks through the basics and gotchas that you should watch out for.
Feature queries, also known as the @supports rule, were introduced as an extension to the CSS2 as part of the CSS Conditional Rules Module Level 3, which was first published as a working draft in 2011. It is a conditional group rule that tests if the browser’s user agent supports CSS property:value pairs, and arbitrary conjunctions (and), disjunctions (or), and negations (not) of them.An excerpt from Cascading Web Design with Feature Queries