Show spin buttons into number input fields of users settings dialog (betaflight#848)

* Added spin button into number input fields of users settings dialog

* CSS style is improved

Author: demvlad

src/css/user_settings_dialog.css

@@ -117,3 +117,13 @@
   position: absolute;
   left: 50px;
 }
+
+.user-settings-dialog input[type="number"]::-webkit-inner-spin-button,
+.user-settings-dialog input[type="number"]::-webkit-outer-spin-button
+{
+  -webkit-appearance: auto !important;
+  appearance: auto !important;
+  opacity: 1 !important;
+  height: auto !important;
+  width: auto !important;
+}