How to resize cart icon only on mobile?

Site URL: http://www.1924.us

I currently have a custom cart icon installed at a 100px by 100px for the desktop view. This size on mobile is too big and I would like to know how to resize say by 50% on only mobile. Thank you! 

Add the following to Design > Custom CSS.

@media only screen and ( max-width : 639px ) {
  
  span.Cart-label:after {
  
    height : calc( 70px / 1.5 );
    width : calc( 42px / 1.5 );
    
    }
    
  }

I tried 50% but it seemed a little small so I went 1.5 on the calc. You can use a calc or just enter in whatever numbers you want.

Let us know how it goes.

This didn't affect my other code sadly, it seems my code is overwriting it. 

// Custom Cart Icon //

.header .header-actions-action--cart .icon {
  background: url(IMAGE) center no-repeat;
  stroke: transparent !important;
  content: "";
  background-size: contain;
width: 60px;
  height: 100px;
  
}

Without my code...

With my code...