chore(dialog): scope passthrough mods to spectrum-Dialog class

Author: marissahuysentruyt

components/dialog/index.css

@@ -48,6 +48,10 @@ governing permissions and limitations under the License.
 
 	/* Hero */
 	--spectrum-standard-dialog-hero-block-size: 140px;
+
+	/* Passthrough for nested component(s) */
+	--mod-buttongroup-justify-content: flex-end;
+	--mod-buttongroup-flex-wrap: nowrap;
 }
 
 .spectrum-Dialog {
@@ -209,13 +213,6 @@ governing permissions and limitations under the License.
 
 .spectrum-Dialog-buttonGroup {
 	grid-area: buttonGroup;
-
-	& > .spectrum-ButtonGroup {
-		/* to override ButtonGroup's justify-content: normal and/or not having footer content,
-    as well as prevent ButtonGroup from wrapping. */
-		--mod-buttongroup-justify-content: flex-end;
-		--mod-buttongroup-flex-wrap: nowrap;
-	}
 }
 
 .spectrum-Dialog-buttonGroup--noFooter {