Flutter Layout Container Margin : <p>I have a problem with my Flutter Layout.</p>

<p>I have a simple container with a Margin right and left of 20.0
Inside this container i have another container.</p>

<p>But this container does not fit to the parent container only on the left side.
I dont know why this happens.</p>

<p>Here is my Code:</p>

<pre><code>  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      backgroundColor: Colors.white,
      body: new Container(
        margin: new EdgeInsets.symmetric(horizontal: 20.0),
        child: new Container(

        )
      ),
    );
  }
</code></pre>

<p><a href="https://i.stack.imgur.com/KtN8B.png" rel="noreferrer">Screenshot of the Problem</a></p>
