diff --git a/core/focus_manager.ts b/core/focus_manager.ts
index 3d0a9347f85..392b2e87c47 100644
--- a/core/focus_manager.ts
+++ b/core/focus_manager.ts
@@ -74,6 +74,22 @@ export class FocusManager {
    */
   static readonly PASSIVE_FOCUS_NODE_CSS_CLASS_NAME = 'blocklyPassiveFocus';
 
+  static readonly ACTIVE_FOCUS_WITHIN_TREE_CSS_CLASS_NAME =
+    'blocklyTreeHasActiveFocus';
+
+  static readonly PASSIVE_FOCUS_WITHIN_TREE_CSS_CLASS_NAME =
+    'blocklyTreeHasPassiveFocus';
+
+  static readonly ACTIVE_FOCUS_WITHIN_SUBTREE_CSS_CLASS_NAME =
+    'blocklySubtreeHasActiveFocus';
+
+  static readonly PASSIVE_FOCUS_WITHIN_SUBTREE_CSS_CLASS_NAME =
+    'blocklySubtreeHasPassiveFocus';
+
+  // Represents the single node that will receive active focus when ephemeral focus ends.
+  static readonly WAITING_FOR_EPHEMERAL_FOCUS_CSS_CLASS_NAME =
+    'blocklyWaitingForEphemeralFocus';
+
   private focusedNode: IFocusableNode | null = null;
   private previouslyFocusedNode: IFocusableNode | null = null;
   private registeredTrees: Array<TreeRegistration> = [];
@@ -365,6 +381,12 @@ export class FocusManager {
     const prevTree = prevNode?.getFocusableTree();
     if (prevNode) {
       this.passivelyFocusNode(prevNode, nextTree);
+      if (this.currentlyHoldsEphemeralFocus) {
+        dom.removeClass(
+          prevNode.getFocusableElement(),
+          FocusManager.WAITING_FOR_EPHEMERAL_FOCUS_CSS_CLASS_NAME,
+        );
+      }
     }
 
     // If there's a focused node in the new node's tree, ensure it's reset.
@@ -382,6 +404,11 @@ export class FocusManager {
     if (!this.currentlyHoldsEphemeralFocus) {
       // Only change the actively focused node if ephemeral state isn't held.
       this.activelyFocusNode(nodeToFocus, prevTree ?? null);
+    } else {
+      dom.addClass(
+        nodeToFocus.getFocusableElement(),
+        FocusManager.WAITING_FOR_EPHEMERAL_FOCUS_CSS_CLASS_NAME,
+      );
     }
     this.updateFocusedNode(nodeToFocus);
     if (mustRestoreUpdatingNode) {
@@ -422,6 +449,10 @@ export class FocusManager {
 
     if (this.focusedNode) {
       this.passivelyFocusNode(this.focusedNode, null);
+      dom.addClass(
+        this.focusedNode.getFocusableElement(),
+        FocusManager.WAITING_FOR_EPHEMERAL_FOCUS_CSS_CLASS_NAME,
+      );
     }
     focusableElement.focus();
 
@@ -438,6 +469,10 @@ export class FocusManager {
 
       if (this.focusedNode) {
         this.activelyFocusNode(this.focusedNode, null);
+        dom.removeClass(
+          this.focusedNode.getFocusableElement(),
+          FocusManager.WAITING_FOR_EPHEMERAL_FOCUS_CSS_CLASS_NAME,
+        );
 
         // Even though focus was restored, check if it's lost again. It's
         // possible for the browser to force focus away from all elements once
@@ -539,6 +574,16 @@ export class FocusManager {
         // longer tabbable now that it holds active focus.
         tree.getRootFocusableNode().getFocusableElement().tabIndex = -1;
       }
+
+      const treeRoot = tree.getRootFocusableNode().getFocusableElement();
+      dom.addClass(
+        treeRoot,
+        FocusManager.ACTIVE_FOCUS_WITHIN_TREE_CSS_CLASS_NAME,
+      );
+      dom.removeClass(
+        treeRoot,
+        FocusManager.PASSIVE_FOCUS_WITHIN_TREE_CSS_CLASS_NAME,
+      );
     }
     node.onNodeFocus();
     this.lockFocusStateChanges = false;
@@ -588,6 +633,16 @@ export class FocusManager {
         // tabbable since it no longer holds active focus.
         tree.getRootFocusableNode().getFocusableElement().tabIndex = 0;
       }
+
+      const treeRoot = tree.getRootFocusableNode().getFocusableElement();
+      dom.addClass(
+        treeRoot,
+        FocusManager.PASSIVE_FOCUS_WITHIN_TREE_CSS_CLASS_NAME,
+      );
+      dom.removeClass(
+        treeRoot,
+        FocusManager.ACTIVE_FOCUS_WITHIN_TREE_CSS_CLASS_NAME,
+      );
     }
     node.onNodeBlur();
     this.lockFocusStateChanges = false;
@@ -633,6 +688,16 @@ export class FocusManager {
     dom.removeClass(element, FocusManager.PASSIVE_FOCUS_NODE_CSS_CLASS_NAME);
   }
 
+  private recomputeSubtreeCssClasses(): void {
+    // Collect all focused elements.
+    // const passiveElems = document.querySelectorAll(
+    //   FocusManager.PASSIVE_FOCUS_NODE_CSS_CLASS_NAME,
+    // );
+    // const activeElem = this.focusedNode?.getFocusableElement() ?? null;
+    // const focusedElems = [...(activeElem ? [activeElem] : []), ...passiveElems];
+    // For each element, collect all... TODO: finish.
+  }
+
   private static focusManager: FocusManager | null = null;
 
   /**