CSS :not(:last-child):after selector

Answer 1

An example using CSS

  ul li:not(:last-child){
        border-right: 1px solid rgba(153, 151, 151, 0.75);
    }

Answer 2

Your example as written works perfectly in Chrome 11 for me. Perhaps your browser just doesn't support the :not() selector?

You may need to use JavaScript or similar to accomplish this cross-browser. jQuery implements :not() in its selector API.