Add rounded corners to videos in in-window fullscreen mode

https://bugs.webkit.org/show_bug.cgi?id=273692
rdar://127496496

Reviewed by Jer Noble.

Add rounded corners to videos in in-window fullscreen mode. This
Requires setting the margins to auto to avoid stretching the
Aspect ratio of the video and removing padding so that the
Rounded corners appear along the video content.

* Source/WebCore/css/fullscreen.css:
(*|*:not(:root):-internal-in-window-fullscreen):

Canonical link: https://commits.webkit.org/278341@main

Source/WebCore/css/fullscreen.css

@@ -70,7 +70,12 @@ iframe:fullscreen {
 }
 
 *|*:not(:root):-internal-in-window-fullscreen {
-    padding: 5% 0%;
+    margin: auto !important;
+    width: auto !important;
+    height: 80vh !important;
+    max-width: 100vw !important;
+    max-height: 100vh !important;
+    border-radius: 20px !important;
 }
 
 *|*:not(:root):-internal-in-window-fullscreen::backdrop {