CSS media query to target only iOS devices

I don't know about targeting iOS as a whole, but to target iOS Safari specifically:

@supports (-webkit-touch-callout: none) {
   /* CSS specific to iOS devices */ 
}

@supports not (-webkit-touch-callout: none) {
   /* CSS for other than iOS devices */ 
}

Apparently as of iOS 13 -webkit-overflow-scrolling no longer responds to @supports, but -webkit-touch-callout still does. Of course that could change in the future...

As mentioned above, the short answer is no. But I'm in need of something similar in the app I'm working on now, yet the areas where the CSS needs to be different are limited to very specific areas of a page.

If you're like me and don't need to serve up an entirely different stylesheet, another option would be to detect a device running iOS in the way described in this question's selected answer: Detect if device is iOS

Once you've detected the iOS device you could add a class to the area you're targeting using Javascript (eg. the document.getElementsByTagName("yourElementHere")[0].setAttribute("class", "iOS-device");, jQuery, PHP or whatever, and style that class accordingly using the pre-existing stylesheet.

.iOS-device {
      style-you-want-to-set: yada;
}

Yes, you can.

@supports (-webkit-touch-callout: none) {
  /* CSS specific to iOS devices */ 
}

@supports not (-webkit-touch-callout: none) {
  /* CSS for other than iOS devices */ 
}

YMMV.

It works because only Safari Mobile implements -webkit-touch-callout: https://developer.mozilla.org/en-US/docs/Web/CSS/-webkit-touch-callout

Please note that @supports does not work in IE. IE will skip both of the above @support blocks above. To find out more see https://hacks.mozilla.org/2016/08/using-feature-queries-in-css/. It is recommended to not use @supports not because of this.

What about Chrome or Firefox on iOS? The reality is these are just skins over the WebKit rendering engine. Hence the above works everywhere on iOS as long as iOS policy does not change. See 2.5.6 in App Store Review Guidelines.

Warning: iOS may remove support for this in any new iOS release in the coming years. You SHOULD try a bit harder to not need the above CSS. An earlier version of this answer used -webkit-overflow-scrolling but a new iOS version removed it. As a commenter pointed out, there are other options to choose from: Go to Supported CSS Properties and search for "Safari on iOS".