Base: Add linear-gradient list-marker demo

Author: https://github.com/MacDue
Commit: 4b9c0aac7a
Pull-request: https://github.com/SerenityOS/serenity/pull/14740
Reviewed-by: https://github.com/AtkinsSJ
Reviewed-by: https://github.com/gmta

Base/res/html/misc/lists.html

@@ -68,6 +68,12 @@
         <li>Another entry</li>
     </ul>
 
+    <p>list-style: linear-gradient(to top left, red, green)</p>
+    <ul style="list-style: linear-gradient(to top left, red, green);">
+        <li>Entry one</li>
+        <li>Another entry</li>
+    </ul>
+
     <p>list-style: inside url(list-item.png)</p>
     <ul style="list-style: inside disc url(custom-list-item.png);">
         <li>Entry one</li>