add bg-dark

Author: cbellone

frontend/src/styles.css

@@ -48,3 +48,15 @@ md-dialog-container.mat-dialog-container {
 .ui-keyboard-button {
   margin: 3px;
 }
+
+/* temporary until we include bootstrap v4.1 */
+
+.bg-dark {
+  background-color: #343a40;
+}
+
+.btn-dark {
+  color: #fff;
+  background-color: #343a40;
+  border-color: #343a40;
+}