HTML Guide for media

Bad value “X” for attribute “media” on element “link”: unrecognized media “X”.

media
link
bad value

The media attribute on a <link> element has not been recognized.

This attribute specified what media the linked resource is optimized for. As an example, the following will link a general stylesheet, and a specific one for printing:

<head>
  <link rel="stylesheet" type="text/css" href="general.css">
  <link rel="stylesheet" type="text/css" href="print.css" media="print">
</head>

Valid values for this attribute include:

all. Default, used for all media.
print. Used for printers and print previews.
screen. Used for computer, tablets or smartphone screens.