title: How to change the color of [part="toggle-button"] in the vaadin-select?
body: <p>My question is: How to change the custom color of <code>[part="toggle-button"]</code> in the <code>vaadin-select</code>?</p>
  
  <p>I've searched how to change it but I cannot get it too. Please help and solve it, thank you!</p>