Change CSS element with JQuery when scroll reaches an anchor point

Try this:

var targetOffset = $("#anchor-point").offset().top;

var $w = $(window).scroll(function(){
    if ( $w.scrollTop() > targetOffset ) {   
        $('#voice2').css({"border-bottom":"2px solid #f4f5f8"});
        $('#voice3').css({"border-bottom":"2px solid #2e375b"});
    } else {
      // ...
    }
});