[M76 Migration] Change background color in tv

[M76 Migration] Change background color in tv

Apply black instread of transparent to background color after below patch is merged.
(https://review.tizen.org/gerrit/#/c/platform/framework/web/chromium-efl/+/226493/)
That patch made proper background color. so change background color to explicitly
set transparent color.

Reference:
https://review.tizen.org/gerrit/#/c/platform/framework/web/wrtjs/+/227901/

Change-Id: I6c8b818cc9da243abc4b50975c7d84f779a0e7ae
Signed-off-by: SangYong Park <sy302.park@samsung.com>