Colum is nearly always right.
However, you should look at the file ehlpdhtm.js.
There are more than 50 references to BSSCPopup, which is the
function that handles text-only popups. Scroll down to this line:
/// Section Begin - Popup (JavaScript 1.0)
A few lines below that you'll see a reference to dropshadow.
I don't have time to explore this further today, but I'm sure
somewhere along the way you can modify or delete the shadow. The
changes will affect all text-only popups in the output.
Start with ehlpdhtml.js in the output directory. Fiddle with
it there as much as you like.
If you settle on something you want to make permanent, for
all future WebHelp ouput, change dhtml.js here:
Program Files/Adobe/Adobe RoboHelp 7/RoboHTML/
Otherwise, you must modify the output file every time you
generate WebHelp.
(As usual, save a copy of the original file, make backups, I
can't guarantee results, this is advice only, etc. etc.)
Plese report back.
Harvey