text: var container = document.querySelector(".container");
  
  container.addEventListener("click", function(event) {
    var element = event.target;
  
    // TODO: Complete function
    if (element.matches(".box")) {
      var state = element.getAttribute("data-state");
  
      if (state === "hidden") {
        element.dataset.state = "visible";
        element.textContent = element.dataset.number;
      } else {
        element.dataset.state = "hidden";
        element.textContent = "";
      }
    }
  });
  