title: Stack on working as expected | z-index (CSS) equivalent
body: <p>I am trying to achieve this(Todo image) but the image is getting hidden. How to bring it on top? I thought using Stack will automatically bring it on top. Is there any z-index equivalent? I have also shared the code below</p>
  <h1>Todo</h1>
  <p><a href="https://i.stack.imgur.com/QivlG.png" rel="noreferrer"><img src="https://i.stack.imgur.com/QivlG.png" alt="enter image description here" /></a></p>
  <h1>In Progress</h1>
  <p><a href="https://i.stack.imgur.com/OIq3c.png" rel="noreferrer"><img src="https://i.stack.imgur.com/OIq3c.png" alt="enter image description here" /></a></p>
  <h1>Code</h1>
  <pre><code>Widget build(BuildContext context) {
      return new Scaffold(
          body: new CustomScrollView(
        slivers: &lt;Widget&gt;[
          new SliverAppBar(
            expandedHeight: 150.0,
            flexibleSpace: new FlexibleSpaceBar(
              background: new Stack(
                alignment: new Alignment(0.0, 2.5),
                children: [
                  new Container(
                    margin: const EdgeInsets.symmetric(vertical: 40.0),
                    decoration: new BoxDecoration(
                        image: new DecorationImage(
                            image: new AssetImage(&quot;images/Theme-pattern.png&quot;))),
                    child: new Column(children: &lt;Widget&gt;[
                      new Text(&quot;Title&quot;, style: new TextStyle(fontSize: 32.0)),
                    ]),
                  ),
                  new Container(
                    decoration: new BoxDecoration(
                        borderRadius:
                            new BorderRadius.all(const Radius.circular(120.0)),
                        color: Colors.white),
                    width: 100.0,
                    child: new Image.asset(&quot;images/photo.png&quot;),
                  )
                ],
              ),
            ),
          ),
        ],
      ));
    }
  </code></pre>