Modifying styles in SlideShow screen environment

I am trying to change the square bullet to circle of the “Item” style in one of the SlideShow templates which I use (Steel).
I tried to edit the style sheet in two ways, one being simply to change (format) the dingbat, the second
that I copied and modified the default definition to the private style sheet of my file.

The problem is that this only changes the style while I am in Working screen environment, but not in
SlideShow environment. I know the different screen environments have different style sheets, but
I do not know how to access them. I appreciate if anyone can tell how the style sheet of the SlideShow
environment can be changed.

When copying the Item style cells out of the built-in Steel stylesheet, be sure to copy all three that are part of the collapsed group. You can then change the CellDingbat option on each of them, as partially shown below.

Thanks very much! In the meantime I also listed out that the Item style cell for the SlideShow environment is also included in the built-in Steel stylesheet and can be copied over to the local definitions and then edited. Your example of the editing the CellDingbat through the Option Inspector was though new to me - thanks!

Now knowing the solution I wonder why not all the different screen environment options are immediately inherited locally when one uses a template for a new slide show - it would be much simpler if one did not need to do this change manually. Anyone from Wolfram to comment? Of course in the continuation I can use my own modified slide to create further new ones, but still.