undo

script.js

@@ -48,8 +48,14 @@ function generateTable() {
 
   table.addEventListener('click', (ev) => {
     if (ev.target.tagName.toLowerCase() == "td" ) {
-        ev.target.style.borderColor = "green";
-        ev.target.style.backgroundColor = "green";
+        let cell = ev.target;
+        if (cell.style.borderColor == "green") {
+          cell.style.borderColor = "black";
+          cell.style.backgroundColor = "white";
+        } else {
+          cell.style.borderColor = "green";
+          cell.style.backgroundColor = "green";
+        }
     }
   });
 }