_modal.scss in bootstrap-5.1.0

- old
+ new

@@ -83,20 +83,10 @@
   outline: 0;
 }
 
 // Modal background
 .modal-backdrop {
-  position: fixed;
-  top: 0;
-  left: 0;
-  z-index: $zindex-modal-backdrop;
-  width: 100vw;
-  height: 100vh;
-  background-color: $modal-backdrop-bg;
-
-  // Fade for backdrop
-  &.fade { opacity: 0; }
-  &.show { opacity: $modal-backdrop-opacity; }
+  @include overlay-backdrop($zindex-modal-backdrop, $modal-backdrop-bg, $modal-backdrop-opacity);
 }
 
 // Modal header
 // Top section of the modal w/ title and dismiss
 .modal-header {