How can I get rid of header's shadow when the elevation = 0?

Hi, this is my first time learning HTML and CSS and I can't figure this out..;( 

I added a box-shadow to the header but I want the shadow to appear only when user scrolls down. 

So the shadow should not appear when the elevation is at 0... How can I achieve this? 

I think it has something to do with   

.MuiPaper-elevation0 {
  box-shadow: none;
}

.. please help me!

Hi. Can you share link to your site? We can check easier