Merge pull request #17120 from kkirsche/patch-5

Add white background to cards by default

scss/_card.scss

@@ -5,6 +5,7 @@
 .card {
   position: relative;
   margin-bottom: $card-spacer-y;
+  background-color: #fff;
   border: $card-border-width solid $card-border-color;
   @include border-radius($card-border-radius);
 }