title: How to add decoration DropdownButton in Flutter
body: <p>I have a dropdown button as you can see below.</p>
  <pre><code>  child: DropdownButton&lt;String&gt;(
                                value: dropDownValue,
                                icon: Icon(Icons.keyboard_arrow_down),
                                iconSize: 15,
                                elevation: 16,
                                style: TextStyle(color: Colors.grey),
                                underline: Container(
                                  decoration: ShapeDecoration(
                                    shape: RoundedRectangleBorder(
                                      side: BorderSide(width: 1.0, style: BorderStyle.solid),
                                      borderRadius: BorderRadius.all(Radius.circular(5.0)),
                                    ),
                                  ),
                              ),
                                onChanged: (String newValue) {
                                  setState(() {
                                    dropDownValue = newValue;
                                  });
                                },
                                items: [dropDownValue,...snapshot.data.data]
                                    .map&lt;DropdownMenuItem&lt;String&gt;&gt;((String value) {
                                  return DropdownMenuItem&lt;String&gt;(
                                    value: value,
                                    child: Text(value.name),
                                  );
                                }).toList(),
                              ),
  </code></pre>
  <p>I want to shape it like in the image by using decoration in Container, but i can't shape it the way i want
  <a href="https://i.stack.imgur.com/whFd6.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/whFd6.jpg" alt="enter image description here" /></a></p>
  <p>But right now this is the image I have. How do I add an edge to my dropdown button? Is there a known way for this?</p>
  <p><a href="https://i.stack.imgur.com/X8qen.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/X8qen.jpg" alt="enter image description here" /></a></p>