visionOS: Fix timeline jump button appearance

Tusker/Screens/Timeline/TimelineJumpButton.swift

@@ -13,15 +13,23 @@ class TimelineJumpButton: UIView {
     var action: ((Mode) async -> Void)?
     
     override var intrinsicContentSize: CGSize {
+        #if os(visionOS)
+        CGSize(width: 44, height: 44)
+        #else
         CGSize(width: UIView.noIntrinsicMetric, height: 44)
+        #endif
     }
     
     private let button: UIButton = {
+        #if os(visionOS)
+        var config = UIButton.Configuration.borderedProminent()
+        #else
         var config = UIButton.Configuration.plain()
-        config.image = UIImage(systemName: "arrow.up")
-        config.contentInsets = .zero
         // We don't want a background for this button, even when accessibility button shapes are enabled, because it's in the navbar.
         config.background.backgroundColor = .clear
+        #endif
+        config.image = UIImage(systemName: "arrow.up")
+        config.contentInsets = .zero
         return UIButton(configuration: config)
     }()
     
@@ -101,8 +109,7 @@ class TimelineJumpButton: UIView {
         }
         self.mode = mode
         
-        var config = UIButton.Configuration.plain()
-        config.contentInsets = .zero
+        var config = button.configuration!
         switch mode {
         case .jump:
             config.image = UIImage(systemName: "arrow.up")