https://validator.w3.org/nu/ when checking the default prosilver style will output some errors for the media quires added through extensions or found in the vanilla template in overall_header.html.

The error will be something like;

Error: Bad value all and (max-width: 700px), all and (max-device-width: 700px) for attribute media on element link: Deprecated media feature max-device-width. For guidance, see the Deprecated Media Features section in the current Media Queries specification.
From line 20, column 1; to line 20, column 158
lesheet"><link href="./styles/prosilver/theme/responsive.css?assets_version=18" rel="stylesheet" media="all and (max-width: 700px), all and (max-device-width: 700px)">

I fixed this on my own style but just thought I'd let you guy know about this so it can be patched.