下面的代码在我想高亮显示的区域的顶部和底部绘制了一个RuleMark，但是，我想把这个区域涂成灰色来显示正常范围，而不是两条线。我该怎么做呢？

import SwiftUI
import Charts

struct ContentView: View {
    
    struct StepCount: Identifiable {
        let id = UUID()
        let weekday: Date
        let steps: Int
        
        init(day: String, steps: Int) {
            let formatter = DateFormatter()
            formatter.dateFormat = "yyyyMMdd"
            
            self.weekday = formatter.date(from: day) ?? Date.distantPast
            self.steps = steps
        }
    }
    
    let currentWeek: [StepCount] = [
        StepCount(day: "20220717", steps: 4200),
        StepCount(day: "20220718", steps: 15000),
        StepCount(day: "20220719", steps: 2800),
        StepCount(day: "20220720", steps: 10800),
        StepCount(day: "20220721", steps: 12370),
        StepCount(day: "20220722", steps: 9500),
        StepCount(day: "20220723", steps: 3700)
    ]
    
    var body: some View {
        VStack {
            Chart {
                ForEach(currentWeek) {
                    LineMark(
                        x: .value("Week Day", $0.weekday, unit: .day),
                        y: .value("Step Count", $0.steps)
                    )
                }
                RuleMark(y: .value("Max of Range", 10000))
                    .foregroundStyle(.red)
                RuleMark(y: .value("Min of Range", 6000))
                    .foregroundStyle(.red)
            }
        }
        .frame(height: 200)
        .padding()
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
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