Fixes #2677 - Tracking protection has transparent top bar (#2693) (#2695

)

Co-authored-by: Bogdan Cernea <bogdan.cernea@softvision.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
(cherry picked from commit dd983e7)

Co-authored-by: Bogdan Cernea <47420700+bogdancernea28@users.noreply.github.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Blockzilla/Tracking Protection/Presentation/SheetModalViewController.swift

@@ -9,7 +9,7 @@ class SheetModalViewController: UIViewController {
 
     private lazy var containerView: UIView = {
         let view = UIView()
-        view.backgroundColor = .clear
+        view.backgroundColor = .systemGroupedBackground
         view.layer.cornerRadius = metrics.cornerRadius
         view.layer.maskedCorners = [.layerMinXMinYCorner, .layerMaxXMinYCorner]
         view.translatesAutoresizingMaskIntoConstraints = false