Switch cards component to grid from flex.

assets/sass/components/cards/_cards.scss

@@ -4,7 +4,7 @@
 
 .cards,
 %cards {
-  @extend %flex-group;
+  @extend %grid-group;
   // Add vertical rhythm margins.
   @include margin-block(1);
 }
@@ -18,6 +18,11 @@
     border-color: var(--color-highlight);
   }
 
+  &--featured {
+    grid-row: span 2;
+    grid-column: span 2;
+  }
+
   &--inverted {
     @extend %link-inverted;
     background: var(--color-border);