Backgrid cell highlight

main.js

                if (this.question_meta.get('correct_prefix') ===
                  correct_answer.get(
                'response').prefix) {
                  this.$el.addClass('correct_td');
                }
                else {
                  this.$el.removeClass('correct_td');
                }
                this.$el.text(selected);
                this.delegateEvents();
                return this;

variables.css

.correct_td {
  background-color: #577432;
}