[Dilettante_Pro]

joker95,

<style>
 .butt {height: 50px;
        width: 100px }
 .cras {background: red }
 .jel  {background: yellow}       
 .bel  {background: white}
 .kn   {border:2px solid blue;
        height: 50px;
        width: 100px}     
</style>
<div class="butt cras" id="red">Красный</div>
<div class="butt jel" id="ark">Желтый</div>
<div class="butt bel" id="well">Белый</div>

<div class="kn"></div>
<script
src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.0/jquery.min.js"></script>
<script>
    $('.butt').on('click', function () {
        var selclass = $(this).attr('class').replace("butt ", ""),
            target = $('.kn');
        target.removeClass();
        target.addClass('kn ' + selclass);
   });
</script>