ho provato a metterlo con #topmenu a:active .... ma senza successo

posto di seguito il codice

/** Topmenu **/
@font-face
{
font-family:fontmenu;
src: url('../font/handsean.ttf'),
url('../font/handsean.eot'); /* IE9+ */
font-weight:bold;
}


#topmenu {

margin: auto;
width: 1000px;
text-align:center;

padding: 0px 0px 0px 0px;

font-size: 18px;
color: #fff;
font-weight: bold;
background:url(../images/top-menu-backbround.png) no-repeat;
overflow: auto;


}

#topmenu ul {
position:relative;
left:0px;
font-family:fontmenu; /*'Helvetica Neue', Helvetica, Arial, sans-serif; font-weight: 400*/
float: left;
padding: 0;
padding-top: 0px;
padding-bottom: 0px;
margin: 0;
list-style: none;
text-align:center;

}


#topmenu a {

background:url(../images/xbottone.png) no-repeat center center;
height:60px;
width:160px;
display: block;
color: #000;
padding-top: 38px;
/*padding-top: 0px;
padding-bottom: 0px;
padding-left: 14px;
padding-right: 14px;
margin-left: 10px;
margin-right: 10px;
margin-bottom: 1px;*/
text-decoration:none;
text-transform: uppercase;

}

#topmenu a:hover {
color: #005E00;
text-decoration: none;
background:url(../images/xbottonehover.png) no-repeat center center;
}



#topmenu li {
float: left;


border-left: 1px solid #339900;

}


#topmenu li:first-child {
border-left: 0px solid #000000;
}



/** Second-level lists **/

#topmenu li ul {
position: absolute;
font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif; font-weight: 400;
font-size: 12px;
width: 162px;
left: -999em; /* "display: none" not seen by screen readers */
border: 0;
margin-left: 0px;
z-index:100;
padding-top: 0px;
padding-bottom: 0px;



}



#topmenu li li,
#topmenu li li:first-child {
border: 0;
border-top: 1px solid #888888;
margin-bottom: -1px; /* iPhone/iPad fix */
}

#topmenu li li a,
#topmenu li.active li a {
width: 162px;
background-color: #666666;
padding-top: 10px;
padding-bottom: 10px;
padding-left: 24px;
margin: 0;
text-transform: none;

}


#topmenu li li:first-child {
margin-top: 14px;
border: 0;
}

#topmenu li ul a {
width: 162px;
}

#topmenu li li a:hover {
color: #fab101;
text-decoration: none;
background-color: #555555;
}



/** Level third and above **/

#topmenu li li li:first-child {
margin-top: 0px;
}

#topmenu li ul ul {
margin: -40px 0 0 200px;
}

#topmenu li:hover ul ul, #topmenu li:hover ul ul ul, #topmenu li.sfhover ul ul, #topmenu li.sfhover ul ul ul {
left: -999em;
}

#topmenu li:hover ul, #topmenu li li:hover ul, #topmenu li li li:hover ul, #topmenu li.sfhover ul, #topmenu li li.sfhover ul, #topmenu li li li.sfhover ul { /* nested under hovered items */
left: auto;
}