How to center a scrollable text in SwiftUI

Question

I have a big text in the middle that can be multiple line. I wrapped it under a scroll view because the text could be very long. When the text does not fit the whole screen, I want to center place the text. I have the following code:

  var body: some View {
    VStack {
      Text("2 / 5")
      Spacer()
      ScrollView([.vertical]) {
        Text("This is a joke. Multiple line is supported. This is a joke. Multiple line is supported. This is a joke. Multiple line is supported. ")
          .fontWeight(.bold)
          .font(.system(.title, design: .rounded))
          .multilineTextAlignment(.center)
      }
      Spacer()
      HStack {
        Button("Prev") {
          // go to prev page
        }
        Spacer()
        Button("Next") {
          // go to next page
        }
      }
    }
  }

However, the text is always on the top. Setting a fixed height works, but I don't want to hardcode any value here. I have also tried putting ScrollView under another VStack, with a spacing, but it has no effects.