.btn-group>.btn:last-child:not(:first-child), .btn-group>.dropdown-toggle:not(:first-child){
    border-bottom-left-radius:3px;
    border-top-left-radius:3px;
}
.btn-group>.btn:first-child:not(:last-child):not(.dropdown-toggle){
    border-bottom-right-radius:3px;
    border-top-right-radius:3px;
}