[IvyKeepMommy]

I'm trying to install and very new at all of this. I'm at the stage in the instructions where it says In the additional CSS, add :

/** DEBUT MGC CHATBOX **/
.mgc_cb_date {
color : #555555;
}

.mgc_cb_me {
color : #FF0000;
}
/** FIN MGC CHATBOX **/

And I'm afraid I'm a bit dense as I don't understand what this means. (I understand I need to add that code, but I don't understand what additional CSS is or how I access it.

Any help would be greatly appreciated.