Hi Robert,
If you click the options button on your grouped layer and choose 'Show properties', this will allow you to edit a number of appearance and visibility settings for the layers within the group. You can also choose the 'Effects' option on the right-hand side of the Map Viewer to add effects to the grouped layers.
I don't believe that it is possible to edit the styles/symbology of multiple grouped layers at a time within Map Viewer, this will need to be done individually.
