Expand toolbox subcategories on keyboard focus

toolbox.js

@@ -4904,6 +4904,16 @@ class CustomCollapsibleToolboxCategory extends Blockly.CollapsibleToolboxCategor
                 this.htmlDiv_?.focus?.();
         }
 
+        ensureKeyboardFocusedSelection_() {
+                this.setExpanded(true);
+
+                const flyout = this.parentToolbox_?.getFlyout?.();
+                if (flyout && !flyout.isVisible?.()) {
+                        const contents = this.getContents?.();
+                        if (contents) flyout.show?.(contents);
+                }
+        }
+
         // Preserve the original icon
         createIconDom_() {
                 const img = document.createElement("img");
@@ -4918,6 +4928,10 @@ class CustomCollapsibleToolboxCategory extends Blockly.CollapsibleToolboxCategor
         setSelected(isSelected) {
                 super.setSelected(isSelected);
 
+                if (isSelected) {
+                        this.ensureKeyboardFocusedSelection_();
+                }
+
                 // Get the category color
                 const categoryColour = this.colour_;
 
@@ -4984,6 +4998,13 @@ class CustomCollapsibleToolboxCategory extends Blockly.CollapsibleToolboxCategor
                         { capture: true },
                 );
 
+                this.rowDiv_.addEventListener("focusin", () => {
+                        if (this.toolboxHasFocus_()) {
+                                this.parentToolbox_?.setSelectedItem?.(this);
+                                this.ensureKeyboardFocusedSelection_();
+                        }
+                });
+
                 return this.htmlDiv_;
         }
 }