Chart with custom image background or transparent chart background

I want to use my custom image as a background for SciChart js.
I tried to put background-image to body of the page.
Then I enabled transparent background via:

sciChartSurface.backgroundCompletelyTransparentEnabled = true;

But it doesn’t work. It does nothing.
Then I tried to put transparent background to SciChart:

sciChartSurface.background = "#00000000";

But it doesn’t work as well. Chart completely disappears in this case.

How can I put my image as a background for SciChart?