Description

The AMP validator is flagging a warning for a CSS media query using the not (prefers-reduced-motion: reduce) syntax. While this syntax is valid in modern browsers, the AMP validator seems to have stricter parsing rules that cause it to be misinterpreted.

This issue impacts accessibility features, as the styles intended for users without a preference for reduced motion are not being applied correctly in the validated AMP version.

@media not (prefers-reduced-motion: reduce) {
  .wp-block-image amp-img.hide {
    visibility: hidden;
  }
}

Reproduction Steps

1. Add the problematic CSS code to the <style amp-custom> tag of an AMP page.
2. Run the page through the official AMP validator (e.g., validator.ampproject.org).
3. Observe the "malformed media query" warning in the validation results.

You can find warnning on

1. https://beebom.com/nyt-strands-today-hints-answers-spangram-august-5-2024/amp/
2. https://wordpress.org/support/topic/gsc-reports-a-warning-for-style-amp-custom/

Relevant Logs

CSS syntax error in tag 'style amp-custom' - malformed media query.

Browser(s) Affected

No response

OS(s) Affected

all

Device(s) Affected

all

AMP Version Affected

2507172035000