title: OpenContainer is showing a background?
body: <p>I'm using openContainer to animate the transition of the FAB to a view/screen - however, there seems to be a box around the fab. How do I remove this ? </p>
  
  <pre><code>OpenContainer(
  
            transitionDuration: Duration(milliseconds: 1000),
            closedBuilder: (BuildContext c, VoidCallback action) =&gt;
                FloatingActionButton(
              elevation: 10,
              backgroundColor: Colors.pink,
  
              onPressed: () {
  
                action();
              },
              child: Icon(Icons.add),
            ),
            openBuilder: (BuildContext c, VoidCallback action) {
              return MyScreen();
            },
            tappable: false,
          ));
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/rw7Xa.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/rw7Xa.png" alt="enter image description here"></a></p>