What is the function of lines 10, 11, 13 and 14?

Question

The class name is set in the code, but the cart.php code already has the same class name. For example, line 72 of cart.php in Section 1-6 sets <div class="box" id ="box"></div>, and className="box" is reset on the tenth line here. Why is this? Why are "box" and "hide" set in line 13?

Answer 1

I really don’t understand. Can anyone give me some advice?