New functions: hide or show second dropdown list

... based on the selection in first dropdown list. Functionality based
on a new `hidden` CSS class

public/css/stylesCustom.css

@@ -32,3 +32,7 @@
   left: 1.25rem;
   z-index: 10;
 }
+
+.hidden {
+  visibility: hidden;
+}

public/js/dropDownList.js

@@ -6,30 +6,52 @@ const dropDownSensorParent = document.querySelector(
 );
 const dropDownSensor = document.querySelector("#drop-down--sensor");
 
+const showSensorDropDownListFromBuildingList = function () {
+  if (dropDownSensorParent.classList.contains("hidden")) {
+    dropDownSensorParent.classList.toggle("hidden");
+  }
+};
+
+const hideSensorDropDownListFromBuildingList = function () {
+  if (!dropDownSensorParent.classList.contains("hidden")) {
+    dropDownSensorParent.classList.toggle("hidden");
+  }
+};
+
+// SET THE INITIAL STATE OF THE DROPDOWN
+hideSensorDropDownListFromBuildingList();
+
 const selectBuildingFromDropDownList = function () {
   const selectedBuilding =
     dropDownBuilding.options[dropDownBuilding.selectedIndex].value;
 
   switch (selectedBuilding) {
     case "none":
+      hideSensorDropDownListFromBuildingList();
       break;
     case "101":
       console.log("Building 101");
+      showSensorDropDownListFromBuildingList();
       break;
     case "102":
       console.log("Building 102");
+      showSensorDropDownListFromBuildingList();
       break;
     case "107":
       console.log("Building 107");
+      showSensorDropDownListFromBuildingList();
       break;
     case "112":
       console.log("Building 112");
+      showSensorDropDownListFromBuildingList();
       break;
     case "125":
       console.log("Building 125");
+      showSensorDropDownListFromBuildingList();
       break;
     case "225":
       console.log("Building 225");
+      showSensorDropDownListFromBuildingList();
       break;
     default:
       console.log("Default case");