How to reduce the font of mainmanu?

hello,
I need to reduce the font of the topmenu (nav). Can you tell me what css change?
thanks you!
Max

For first level items:

template_css.css:

#nav a {
display: block;
padding: 0px 8px;
margin: 0;
text-decoration: none;
font-family: "Lucida Sans Unicode", "Lucida Grande", sans-serif;
font-size: 17px;
text-transform: uppercase;
}

for drop-down level:

#nav li:hover ul li a {
margin: 0px 5px;
text-transform: none;
font-family: Arial, Helvetica, sans-serif;
font-size: 14px;
}