title: How to change background color of Stepper widget to transparent color?
body: <p>Stepper widget's background color is transparent at the Vertical type. When change type like StepperType.horizontal, stepper has white-grey background color. How could I change that background color at the horizontal axis?</p>
  
  <blockquote>
    <p>Here is my sample code:</p>
  </blockquote>
  
  <pre><code>Container(
     width: _width,
     child: Stepper(
        type: StepperType.horizontal,
        steps: [
          Step(
            title: Text("First"),
            content: Text("This is our first example."),
          ),
          Step(
            title: Text("Second"),
            content: Text("This is our second example."),
          ),
        ],
      ),
    ),
  </code></pre>