UI improvements...

added icons from original doc (they still need minifying).
removed highlight demo.
added shift-toggle for opacity.
added escape to end editing.

script.js

@@ -0,0 +1,18 @@
+const gridItems = document.querySelectorAll('.grid-item');
+
+function toggleItem(event) {
+    if (event.metaKey || event.shiftKey) {
+        const toggleThis = event.target.closest('.grid-item');
+        toggleThis?.classList.toggle('lo');   
+    }
+}
+
+for (const item of gridItems) {
+  item.addEventListener('click', toggleItem);
+}
+
+document.addEventListener('keydown', event => {
+    if (event.key === 'Escape') {
+      document.activeElement.blur();
+    }
+  });