Class and ID names

Apply a style to all elements

* { 
  margin: 0; 
  padding: 0; 
  border: 0; 
}

Multiple Class Names

Apply style to different classes

Comma seperate them

.my_menu_rss a, .my_menu_rss a:hover {
Apply style to elements which have all the specified classes  
.my_menu_rss a.my_menu_rss a:hover {

(Note there is NO comma between them)