@damngoodiam @standupurology Are you using the wp-appbox plugin?
If so, I believe this is the same thing that was reported in two other topics:
https://wordpress.org/support/topic/amp-css-syntax-error-in-tag-style-amp-custom-2/
https://wordpress.org/support/topic/css-syntax-error-in-tag-style-amp-custom-11/
In the wp-appbox plugin specifically. There is this CSS:
@media only screen and (-webkit-min-device-pixel-ratio: 1.5), only screen and (min--moz-device-pixel-ratio: 1.5), only screen and (min-resolution: 240dpi) {
div.googleplay a.apptitle {
background: url(../img/googleplay-small.png);
}
}
You can see the code in wp-appbox here: https://plugins.trac.wordpress.org/browser/wp-appbox/tags/4.3.9/css/styles.css#L538
The min--moz-device-pixel-ratio here is invalid. From looking at the MDN docs, this min--moz-device-pixel-ratio is ancient code that only works in Firefox versions before 16.
Therefore, you should contact wp-appbox to have them remove this obsolete code.
Their support forum: https://wordpress.org/support/plugin/wp-appbox/
Otherwise, if you aren’t using that plugin specifically, the fix would be the same if it’s in another plugin or theme.
It appears that Google Search Console has some additional CSS validation that is being performed beyond what the AMP validator is checking. I’ll see if I can get someone on the Search Console team to take a look.
Nevertheless, the issue here is reported as a warning. It’s not preventing your AMP pages from being indexed, as it is not an AMP validation error.
