Make background a scrollable png for flutter

I am making a flutter website, where on mobile I would want to have a png image that fits the width of the device, but it keeps the ratio of the image, and makes it scrollable. This is my code:

 child: Stack(children: [
        SingleChildScrollView(
          child: Container(
            color: Colors.red,
            width: width,
            height: height,
            child: DecoratedBox(
                decoration: BoxDecoration(
              image: DecorationImage(
                  image: AssetImage(mobileBackground),
                  fit: BoxFit.fitWidth),
            )
                //height: height,
                ),
          ),
        ),

This doesn't scroll though. Is there a way to fix this? Thanks.