code: function findCellByLabel(monthElement, day) {
      var tds = monthElement.querySelectorAll('td');
      var td;
  
      for (var i = 0; i < tds.length; i++) {
        td = tds[i];
        if (td.textContent === day.toString()) {
          return td;
        }
      }
    }
docs: Finds a td given a label.