How to remove/add a class from one element and add/remove a class to another?

Question

JavaScript

How to make that when you click on "Set 2" closes "Set 1" and vice versa? That is, so that when you click on "Set 1" from "Set 2" the .opened class is removed and the .closed class appears

Answer 1

$('.section').on('click', '.control-label', function() {
  $(this)
    .closest('.box')
    .toggleClass('opened')
    .siblings()
    .removeClass('opened');
});

The additional closed class is not needed, let the content be hidden by default. Accordingly, the styles need to be tweaked a bit:

.box .list {
  display: none;
}
.box.opened .list {
  display: block;
}