title: Prevent BoxShadow from being clipped by parent
body: <p>I'm building my own material-like card with a box shadow. I want to have several of these combined in a <code>PageView</code>, so that I can swipe between cards - each <code>Card</code> should fill out the entire width of the screen.
  The cards are having a <code>BoxShadow</code> as decoration, however when inserting the <code>Card</code> into the <code>PageView</code> (or any other wrapping widget), the <code>BoxShadow</code> will disappear as it is clipped by the <code>PageView</code>'s bounding box.</p>
  
  <p>This can be fixed by wrapping the <code>Card</code> into a <code>Padding</code>, but that's not what I want since I prefer the padding to be given by the outermost widget to all child widgets of that entire view - so that in case my padding ever changes I don't have to change every single widget.</p>
  
  <p>This is how my <code>Card</code> code looks like:</p>
  
  <pre><code>class Card extends StatelessWidget {
    final Widget child;
    final EdgeInsetsGeometry padding;
  
    Card({@required this.child, this.padding});
  
    @override
    Widget build(BuildContext context) {
      return Container(
        decoration: BoxDecoration(color: Colors.white, boxShadow: &lt;BoxShadow&gt;[
          BoxShadow(color: Color.fromRGBO(0, 0, 0, 0.1), blurRadius: 14.0),
          BoxShadow(
              color: Color.fromRGBO(0, 0, 0, 0.1),
              offset: Offset(0, 2),
              blurRadius: 2.0)
        ]),
        child: Padding(
          padding: padding ?? EdgeInsets.all(20),
          child: this.child,
        ),
      );
    }
  }
  </code></pre>
  
  <p>Wrapping several of these results in the described clipping behavior. </p>
  
  <p><strong>Is there a way of telling Flutter not to clip whatever is "leaking" out of the bounding box?</strong>
  The same behavior happens when positioning widgets on a stack out of bounce.</p>