quaggaJS/example/sass/phone/_overlay.scss

@include phone {
  $overlayWidth: $videoWidth;
  $overlayHeadline: 16px;
  $overlayHeadlineMargin: 14px;
  $overlayPadding: 20px;
  $overlayHeight: $videoHeight + $overlayHeadlineMargin + $overlayHeadline;
  
  .overlay.scanner {
    width: $overlayWidth;
    height: $overlayHeight;
    padding: $overlayPadding;
    margin-top: -($overlayHeight)/2 - $overlayPadding;
    margin-left: -($overlayWidth + 2*$overlayPadding)/2;
    background-color: $overlayBackground;
    @include box-shadow(none);
    
    & > .header{
      margin-bottom: $overlayHeadlineMargin;
      h4, .close{
        line-height: $overlayHeadline;
      }
      .close{
        height: $overlayHeadline;
        width: $overlayHeadline;
      }
    }
  }
}