.ui-button .ui-icon.ui-icon-checkbox-checked {
    background-image: url(../images/checkbox-checked.png);
    width: 16px;
    height: 16px;
}

.ui-button.ui-state-hover .ui-icon.ui-icon-checkbox-checked {
    background-image: url(../images/checkbox-checked.png );
    width: 16px;
    height: 16px;
}

.ui-button .ui-icon.ui-icon-checkbox-unchecked {
    background-image: url(../images/checkbox-unchecked.png);
    width: 16px;
    height: 16px;
}

.ui-button.ui-state-hover .ui-icon.ui-icon-checkbox-unchecked {
    background-image: url(../images/checkbox-unchecked.png );
    width: 16px;
    height: 16px;
}