title: Flutter UI: Absolute positioned element with fixed height and 100% width
body: <p>In flutter, I'd like to have a Container with a fixed height and 100% width.</p>
  
  <p>To accomplish this, I used:</p>
  
  <pre><code>              Row(
                  children: &lt;Widget&gt;[
                    Flexible(
                      child: Container(
                        color: Colors.blue,
                        height: 40.0,
                      ),
                    ),
                  ],
                ),
  </code></pre>
  
  <p>Now, I'd like to offset this row a few pixels offscreen.  To accomplish this, I'm attempting to use:</p>
  
  <pre><code>        Stack(
            children: &lt;Widget&gt;[
              Positioned(
                left: -5.0,
                child: Row(
                  children: &lt;Widget&gt;[
                    Flexible(
                      child: Container(
                        color: Colors.blue,
                        height: 40.0,
                      ),
                    ),
                  ],
                ),
              ),
            ],
          ),
  </code></pre>
  
  <p>This gives me the error:</p>
  
  <p><strong>The following assertion was thrown during performLayout(): RenderFlex children have non-zero flex but incoming width constraints are unbounded.</strong></p>
  
  <p>How would I create this layout effect?</p>