add cross browser support for image-set() css ref in alternative image formats example

Author: digi-booster

images/image-set-type.html

@@ -16,6 +16,9 @@
 
     <style class="editable">
        .box {
+           background-image: -webkit-image-set(
+            url("large-balloons.avif") type("image/avif"),
+            url("large-balloons.jpg") type("image/jpeg"));
           background-image: image-set(
             url("large-balloons.avif") type("image/avif"),
             url("large-balloons.jpg") type("image/jpeg"));
@@ -46,4 +49,4 @@
 </body>
 <script src="playable.js"></script>
 
-</html>
+</html>