diff --git a/scss/_modal.scss b/scss/_modal.scss
index fa76b0ea5649..65b61d90c297 100644
--- a/scss/_modal.scss
+++ b/scss/_modal.scss
@@ -18,11 +18,11 @@
 .modal {
   position: fixed;
   top: 0;
-  right: 0;
-  bottom: 0;
   left: 0;
   z-index: $zindex-modal;
   display: none;
+  width: 100%;
+  height: 100%;
   overflow: hidden;
   // Prevent Chrome on Windows from adding a focus outline. For details, see
   // https://github.com/twbs/bootstrap/pull/10951.
@@ -84,10 +84,10 @@
 .modal-backdrop {
   position: fixed;
   top: 0;
-  right: 0;
-  bottom: 0;
   left: 0;
   z-index: $zindex-modal-backdrop;
+  width: 100vw;
+  height: 100vh;
   background-color: $modal-backdrop-bg;
 
   // Fade for backdrop