fix(FEC-11271):displaying .VTT captions not working properly for belo…

…w video layout (#4228)

Issue:
when setting the captions layout to "below video" and playing .vtt captions- the captions are placed on the video as "on top" layout, instead of inside the container below the video.

Solution:
forcing inset=0 when layout=below video. In addition, added position=relative to parent class so captions will be placed according to the caption container and not to the video holder.

Solves FEC-11271

modules/KalturaSupport/resources/mw.ClosedCaptions.js

@@ -775,8 +775,13 @@
 					.css('pointer-events', 'auto')
 					.css('z-index', '3')
 					.css('pointer-events', 'none')
+					.css('position', 'relative')
 				);
 
+			if (this.getConfig('layout') === 'below') {
+				$(caption.content).css('inset', '0px');
+			}
+
 			this.displayTextTarget($textTarget);
 
 			var captionDiv = $('.caption div');