I am trying to implement multiSelect combobx with checkbox selection. PFB the snapshot :

Attachment 41332

I have used
listConfig : {        baseCls: 'z-myboundlist'
in combobox. And in ext-all.css, have put
.z-myboundlist-selected { }
to modify css and place the checked image of checkbox in background, when that particular combo box list is selected. It is working fine as you can see the checkbox checked in the above diagram.

However, what I need is an unchecked checkbox image in the remaining list items within the combo box. I added
.z-myboundlist-item {}
in ext-all.css, but it is not working.

When I do an inspect element in the combo box list items, I get this :
<li role="option" class="x-boundlist-item">South Korea</li>
I want to know, why ''.z-myboundlist-item' is not getting added in class, and still 'x-boundlist-item'is being shown.

I cannot add the unchecked chekbox image in x-boundlist-item class, since it will be added in all the combo box instances in the page. I want it to be specific to a single specific combo box.

Please help.