title: SwiftUi Preview show no color
body: <p>I'm a newbie in SwiftUI and I have a little question. </p>
  
  <p>I have made an Code for a Menu Bar, but when I run the Preview the "Gradient" isn't show. </p>
  
  <p>Everything is white in preview. </p>
  
  <p><a href="https://i.stack.imgur.com/pZNYd.png" rel="nofollow noreferrer">code</a></p>
  
  <p><a href="https://i.stack.imgur.com/R8nq0.png" rel="nofollow noreferrer">preview</a></p>
  
  <p>I hope u can help me guys! </p>
  
  <p>Thanks</p>