external css for new created module

Hello drupal champs,

I have query regarding how to change style sheet of new created module..

Step 1:
I have created module name as logo
with three files. logo.info, logo.module and logo.css

Step 2:
i have added this new module in a block(Top - Left).

Step 3:
then added new style sheet for this module using function drupal_add_css in file template.php

and created .Block class in css.
here all block along with logo block get effected with this .Block class and i don't want any border or block header name here..i want simple logo here..
how to disable .Block class effect in this logo block???

Thanks,
Mitesh