Fix sidebar appearance

Author: ivanvorobei

Example iOS/Controllers/SideBarController.swift

@@ -77,6 +77,7 @@ class SideBarSplitController: UISplitViewController {
     override func viewDidLoad() {
         super.viewDidLoad()
 
+        primaryBackgroundStyle = .sidebar
         preferredDisplayMode = .oneBesideSecondary
         presentsWithGesture = false
         preferredSplitBehavior = .tile

Sources/SPDiffable/Collection/SPDiffableSideBarController.swift

@@ -56,7 +56,6 @@ open class SPDiffableSideBarController: UIViewController, UICollectionViewDelega
 
         let layout = UICollectionViewCompositionalLayout { [weak self] (section, layoutEnvironment) -> NSCollectionLayoutSection? in
             var configuration = UICollectionLayoutListConfiguration(appearance: .sidebar)
-            configuration.backgroundColor = UIColor.secondarySystemBackground
             let header = self?.diffableDataSource?.snapshot().sectionIdentifiers[section].header
             configuration.headerMode = (header == nil) ? .none : .firstItemInSection
             let footer = self?.diffableDataSource?.snapshot().sectionIdentifiers[section].footer