title: How to remove arrow icon from spinner without removing bottom line
body: <p>I need to remove the arrow icon at the right of <code>dropdown spinner</code>. </p>
  
  <p>I want to display it just like <code>edittext</code> field. </p>
  
  <p>I treid <code>background="@null"</code>, but it removes both bottom line and arrow icon.</p>
  
  <p>I just want to remove the arrow icon. </p>