Change the CSS position property of controller to relative

Change the CSS position property of controller to relative

[Title] Change the CSS position property of controller to relative
[Issue] N/A
[Problem] If panel position is fixed, siblings is difficult to calculate each position.
[Cause] The position of media controller is currently fixed.
[Solution] we replaced the position property from fixed to relative.

Change-Id: I0a026120d2fac1d88d600db8eb74c0e73fae2462