Add dark content card variant

styles/40-components-cards.css

@@ -23,6 +23,12 @@
   background: var(--surface-card);
 }
 
+.sg-card.sg-card--content-card-dark {
+  --surface-card: var(--surface-card-group);
+  --surface-card-body: var(--surface-card-group);
+  --text-card-body: var(--text-card-header);
+}
+
 .sg-card.sg-card--overlay-host {
   overflow: visible;
 }