How to change focus to dropdown panel after opening dropdowns in slash command. And set one plugin as default to navigate between plugins

Question

_getPluginListItemsDefinitons() {
        const editor = this.editor;
        const locale = editor.locale;

        this._dropdown = createDropdown(locale);
    
        this._commandItems = [];
        const commandNames = ['bold','italic','underline','horizontalLine','bulletedList','numberedList','insertTable','codeBlock','paragraph','table','subscript','superscript','widgetBox'];
    
        commandNames.forEach((commandName) => {
            const command = editor.commands.get(commandName);
            if (command) {
                const buttonModel = {
                    type: 'button',
                    model: {
                        label: commandName.charAt(0).toUpperCase() + commandName.slice(1),
                        withText: true,
                        icon: icons[commandName] || icons.cog,
                        commandName: commandName,
                    },
                };
                this._commandItems.push(buttonModel);
            }
        });
    
        this._commandItems.sort((a, b) => {
            return a.model.label.localeCompare(b.model.label);
        });
    
        this._addItemsToDropdown(this._commandItems);
        this._createCustomToClass();

        this._dropdown.isOpen = true;
        console.log("dropdown",this._dropdown)
        if(this._dropdown.isOpen === true){
            this._dropdown.render();
            this.focusTracker = new FocusTracker();
            console.log("focusTracker", this.focusTracker)
            const elementFocus = this._dropdown.panelView;
            this.focusTracker.isFocused = true
            this.focusTracker.focusedElement = elementFocus
            this.focusables = new ViewCollection();
            console.log("focusables", this.focusables)
            
            const focusableElements = this._dropdown.element.querySelectorAll('button, input, [tabindex]:not([tabindex="-1"])');
            focusableElements.forEach(element => {
                const view = new View(element); 
                this.focusables.add(view);
            });
            const firstButton = focusableElements[1];
                if (firstButton) {
                    firstButton.focus();
                    firstButton.style.setProperty('background-color', '#007bff', 'important');
                    firstButton.style.setProperty('color', '#ffff', 'important');
                }
            this.keystrokes = new KeystrokeHandler();
            this.focusCycler = new FocusCycler({
                focusables: focusableElements,
                focusTracker: this._dropdown.panelView,
                keystrokeHandler: this.keystrokes,
                actions: {
                    focusPrevious: ['arrowup'],
                    focusNext: ['arrowdown']
                }
            });
            console.log("focus cycler", this.focusCycler);
            this._dropdown.panelView.on('keydown', (evt, data) => {
                const keyCode = data.keyCode;
                if (keyCode === 38) { 
                    this.focusCycler.focusPrevious(); 
                    data.preventDefault();
                } else if (keyCode === 40) {
                    this.focusCycler.focusNext(); 
                    data.preventDefault();
                }
            });
        }

        this.listenTo(this._dropdown, 'execute', (evt, data) => {
            const commandName = evt.source.commandName;
            if (commandName) {
                this.customExecution(commandName);
                if (!this._dropdown.isOpen) {
                    editor.editing.view.focus();
                }
            }
            this._dropdown.isOpen = false;
            this.hideDropdown();
        });
    }

the focus is not changing to the slash command dropdown.The focus should change from the editor to dropdown panel after dropdown opened. it's not like user clicking the toolbar button and showing the dropdown. i am showing the dropdown after enter (.) special character.