The @viewport rule was introduced in CSS to define how a web page should be displayed on different devices. However, its use is not recommended for several reasons, and the viewport tag remains the standard way to handle viewport settings.

The @viewport rule had minimal adoption and is now deprecated in major browsers like Chrome and Firefox. The tag, however, is widely supported. Use the viewport tag in the of your document.

Do not use @viewport in CSS because it is not widely supported. It can cause rendering issues. And it is deprecated.