Bug 1095826 - [RTL][Video] Thumbnail images do not appear

Good point. There was also an inconsistency where there was a margin of 1.6rem top and bottom and then padding-left of 1rem. I don't see why we would want or need to mix margin and padding, so I've changed it to 'margin: 1.6rem 1rem'. Having one rem margin left and right helps with rtl support also.