A CSS descriptor sets specific properties and values of an at-rule (@-rule) element, dictating its appearance and behavior on a webpage. An at-rule is a command preceded by the "@" symbol. CSS at-rules help web developers control specific attributes of code snippets, allowing granular control over a page’s layout, behavior, and overall styling.

Consider the at-rule @media, which applies different styles for various media types and screen sizes. Here’s an example code snippet of how a CSS descriptor can work within this at-rule:

@media screen and (max-width: 600px) {

  body {

    background-color: lightblue;



In this example, @media screen and (max-width: 600px, is the at-rule. It applies the descriptor body { background-color: lightblue; } when the condition of the viewport being 600 pixels wide or less is met. The descriptor defines the body’s background color to be light blue.

Developers and designers use descriptors to style elements for various screen sizes, define media queries, import stylesheets from external sources, and process different media types. As a result, they enable developers to craft responsive, user-friendly designs that enhance the browsing experience for site visitors.

Visit Webflow University to learn how to create responsive designs for your website. Explore ways to design with clean code in markup languages like HTML and CSS for an optimized blend of flair and functionality.

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