title: Remove underline from DropdownButtonFormField
body: <p>How can I remove the underline from DropdownButtonFormField (check photo below), I have tried various combinations of options with InputDecortaion couldn't find any way.</p>
  
  <p><a href="https://i.stack.imgur.com/74h0g.png" rel="noreferrer"><img src="https://i.stack.imgur.com/74h0g.png" alt="DropdownButtonFormField"></a></p>
  
  <pre><code>SizedBox(
    width: 100.0,
    child: DropdownButtonFormField&lt;int&gt;(
      decoration: InputDecoration(
          border: UnderlineInputBorder(
              borderSide:
                  BorderSide(color: Colors.white))),
      value: 2,
      items: &lt;DropdownMenuItem&lt;int&gt;&gt;[
        DropdownMenuItem&lt;int&gt;(
          value: 1,
          child: Text("Owner"),
        ),
        DropdownMenuItem&lt;int&gt;(
          value: 2,
          child: Text("Member"),
        ),
      ],
    ),
  </code></pre>