label[for="value-here"]{
  /* styles */
}

label[for="for_value"] {
  /* CSS Properties */
}

<label class="new-label"></label>

.new-label {
 /* Styles */
}

<label class="my_label" id="my_label_id" for="rn_Select"><span></span></label>

.my_label{
    /*style goes here*/
    }

   #my_label_id{
    /*style goes here*/
   }

input#your_input_id + label{
   /*css rules*/
}