Help with Custom trigger on MultiCombo

[joao.msdn]

Hello, i'm with a problem, im trying to change the default trigger image of a multicombo.

i've half succed, i make 2 triggers image side by side.

for this i put this tag on a multicombo TriggerClass="triggerCbo"

my css:

.triggerCbo
{
    background-image: url('../img/trigger2.png') !important;
    background-repeat: no-repeat;    
} 


it works, but when i click on the trigger the trigger desapears.

how can i fix it?

thanks

[joao.msdn]

Does someone knows how can i fix it or other way to do this?

thanks a lol