SwiftUI 文本字段 - 如何在编辑模式下将文本字段的背景颜色设置为清除

为了配合其他控件，我的文本字段获得了框架，其高度大于文本本身。标准视图显示在带有自定义占位符的示例上部文本字段中。当我单击 Textfield 时，较小的文本区域本身具有灰色背景：

如何将此文本背景设置为清晰的颜色？

    struct TestView: View {

    @State var city: String
    @State var street: String

    var body: some View {
        VStack{
            ZStack(alignment: .center) {
                if city.isEmpty { Text("Bitte Namen eingeben")
                    .font(.system(size: 24, weight: .heavy, design: .default))
                    .foregroundColor(Color( red: 1.0, green: 0.0, blue: 0.0, opacity: 0.3))
                }
            TextField("", text: self.$city)
                .textFieldStyle(CustomTFStyle())
            }

            ZStack(alignment: .center) {
                if street.isEmpty { Text("Bitte Strasse eingeben")
                    .font(.system(size: 24, weight: .heavy, design: .default))
                    .foregroundColor(Color( red: 1.0, green: 0.0, blue: 0.0, opacity: 0.3))
                }
            TextField("", text: self.$street)
                .textFieldStyle(CustomTFStyle())
            }
        }
    }
}

    public struct CustomTFStyle : TextFieldStyle {
    public func _body(configuration: TextField<Self._Label>) -> some View {
        configuration
            .accentColor(.black)
                .frame(width: 300, height: 70, alignment: .center)
                .border(Color.gray, width: 4)
             .font(.system(size: 30, weight: .heavy, design: .default))
            .clipShape(RoundedRectangle(cornerRadius: 12))
            .shadow(radius: 12)
            .foregroundColor(.black)

    }
}