Bug 248724

Safari does not take into account the "media" attribute in the <link> tag to prioritize the loading of CSS files. All browsers based on based Chromium and Firefox do this correctly.

The browser should respect the "media" attribute and give more priority to files associated with the current @media conditions. And also do not wait for unnecessary files and do not delay rendering while they are loading.

This behavior is also described and encouraged in this MDN article: 
https://developer.mozilla.org/en-US/docs/Learn/Performance/CSS
And here:
https://nednex.com/en/split-your-css-to-media-related-files-to-improve-performance-significantly/

Thank you so much for your invaluable work, I hope this important optimization will be in WebKit as soon as possible.