resources/tools/dash/app/pal/static/sass/bootstrap/mixins/_backdrop.scss

   1 // Shared between modals and offcanvases
   2 @mixin overlay-backdrop($zindex, $backdrop-bg, $backdrop-opacity) {
   3   position: fixed;
   4   top: 0;
   5   left: 0;
   6   z-index: $zindex;
   7   width: 100vw;
   8   height: 100vh;
   9   background-color: $backdrop-bg;
  10
  11   // Fade for backdrop
  12   &.fade { opacity: 0; }
  13   &.show { opacity: $backdrop-opacity; }
  14 }