Didn't get much help on the module usage forum so I thought I'd try here.

In Shoutbox 3

As I understand it if you delete the .css file from the module it defaults to the main site .css
If you amend/create a "shoutbox.css" this will overide the main site .css

This is clear and it all works as it says on the box!

However what do I need to do to get the popup only to see the shoutbox.css and the mainsite block revert to the default css.

In this way I can make the shoutbox popup a little more descreet and ensure that the shoutbox mainsite block is in keeping with the main theme.

or can I create a second css file and link this specically to the popup only?

cou can create a second css file and link it, or find the popup template and add the css inline.

Thanks, however

In words of few Syllables can you advise which solution would be easier.
I've had a go but with limited sucess so far. (ie it didn't work)

Just need a little more detail in terms of identifying either the right links to amend or the right template to doctor.

I've never used that module, so I can't help you there. But, if you go to system admin>templates, and clone your template set, you should be able to find the template you need to edit. You can either edit it directly, or copy/paste it into your own editor, make changes and copy/paste it back.