move the card-block flex action up to all card-blocks

this allows us to easily scale card blocks in groups and decks, without repeating it in our css

scss/_card.scss

@@ -12,6 +12,9 @@
 }
 
 .card-block {
+  // Enable `flex-grow: 1` for decks and groups so that card blocks take up
+  // as much space as possible, ensuring footers are aligned to the bottom.
+  flex: 1 1 auto;
   padding: $card-spacer-x;
 }
 
@@ -204,10 +207,6 @@
       margin-bottom: 0; // Margin balancing
       margin-left: $card-deck-margin;
     }
-
-    .card-block {
-      flex-grow: 1;
-    }
   }
 }