.tok-errors-tbar-icon {
  background: url(images/errors_toolbar_ico.jpg) no-repeat;
}

.tok-errors-wnd-icon{
  background-image: url(images/errors-mini-ico.png);  
}
.tok-errors-wnd-s-icon{
  background-image: url(images/s-errors-mini-ico.png);  
}