Hi Maurice,
The CSS that Justin posted in that thread is what is generated for use with the Mobile Article Explorer by default. In order to see a change, you would need to change the values in that CSS.
Make the change locally and then upload it to your server. Then you should see the change. You might need to clear your cache or you could use a query string while you're testing.
To change the color of the drop shadow, you can use the following CSS:
#colorbox{
box-shadow:0 0 10px 10px #ff0000;
}
The CSS above changes the drop shadow color to a bright red (so you know that it has changed). You can change the hex value for the color to make the color that you need.
I don't have CSS to change the background color.
Another approach would be to make a pop-up that contains the content formatted how you want.