Sorted it, this is the CSS I ended up using:
‘/* Menu modifications */
/* changes menu font and size */
#header-menu > li {
font-size: 10pt;
margin: 0 0 0 2px;
height: 25px !important;
padding 0 0px;
}
/* moves menu to top of page and fixes it in position */
#header-menu-wrap {
margin-top: -161px !important;
z-index: 15;
position: fixed !important;
width: 97% !important;
}
#container {
margin-top: 25px;
}
/* reduces the height and font of the sub-menu items in the drop down */
#nav .menu ul li a,
#nav .menu ul li a:visited{
padding: 5px;
}
#nav .menu li ul ul {
margin-top: -28px;
}’