MenuItems don't come with any styling by default! You'll probably want to make your own component which wraps them and adds your own application's style to them like this.
349114
function LI(props) {
  return (
    <MenuItem
      style={{cursor: 'pointer', userSelect: 'none'}}
      highlightedStyle={{background: 'gray'}}
      onItemChosen={e => {
        console.log(`selected ${props.children}, byKeyboard: ${String(e.byKeyboard)}`);
      }}
      {...props}
    />
  );
}
280797
private MenuItem addInternal(int group, int id, int categoryOrder, CharSequence title) {
        final int ordering = getOrdering(categoryOrder);

        final MenuItemImpl item = new MenuItemImpl(this, group, id, categoryOrder,
                ordering, title, mDefaultShowAsAction);

        if (mCurrentMenuInfo != null) {
            // Pass along the current menu info
            item.setMenuInfo(mCurrentMenuInfo);
        }

        mItems.add(findInsertIndex(mItems, ordering), item);
        onItemsChanged(true);

        return item;
    }
672507
private void buildUI() {
		add(new WSkipLinks());

		// the application header
		add(headerPanel);
		headerPanel.add(new UtilityBar());
		headerPanel.add(new WHeading(HeadingLevel.H1, "WComponents"));

		// mainPanel holds the menu and the actual example.
		add(mainPanel);
		mainPanel.add(menuPanel);
		mainPanel.add(exampleSection);

		// An application footer?
		WPanel footer = new WPanel(WPanel.Type.FOOTER);
		footer.add(lastLoaded);
		add(footer);
		add(new WAjaxControl(menuPanel.getTree(), new AjaxTarget[]{menuPanel.getMenu(), exampleSection}));
	}
416377
private ColorItem buildColorItem(Message menuItem) {
        final int colorId = (int) ((NumberField) menuItem.arguments.get(1)).getValue();
        final String label = ((StringField) menuItem.arguments.get(3)).getValue();
        return buildColorItem(colorId, label);
    }
450031
def add_context_menu_items(self, items, replace_items=False):
        '''
        '''
        for label, action in items:
            assert isinstance(label, basestring)
            assert isinstance(action, basestring)
        if replace_items:
            self._context_menu_items = []
        self._context_menu_items.extend(items)
        self._listitem.addContextMenuItems(items, replace_items)
452655
private void fillMenu() {
        // Create a selection listener to handle when the
        // user selects a warning severity.
        SelectionListener menuItemSelectionListener = new SelectionAdapter() {
            /*
             * (non-Javadoc)
             *
             * @see
             * org.eclipse.swt.events.SelectionAdapter#widgetSelected(org.eclipse
             * .swt.events.SelectionEvent)
             */
            @Override
            public void widgetSelected(SelectionEvent e) {
                Widget w = e.widget;
                int index;
                for (index = 0; index < severityItemList.length; ++index) {
                    if (w == severityItemList[index]) {
                        break;
                    }
                }

                if (index < severityItemList.length) {
                    if (bugInstance != null) {
                        bugInstance.setProperty(BugProperty.SEVERITY, String.valueOf(index + 1));
                    }
                }
            }
        };

        severityItemList = new MenuItem[SEVERITY_LABEL_LIST.length];
        for (int i = 0; i < SEVERITY_LABEL_LIST.length; ++i) {
            MenuItem menuItem = new MenuItem(menu, SWT.RADIO);
            menuItem.setText(SEVERITY_LABEL_LIST[i]);
            menuItem.addSelectionListener(menuItemSelectionListener);

            severityItemList[i] = menuItem;
        }

        // Keep menu in sync with current BugInstance.
        menu.addMenuListener(new MenuAdapter() {
            /*
             * (non-Javadoc)
             *
             * @see
             * org.eclipse.swt.events.MenuAdapter#menuShown(org.eclipse.swt.
             * events.MenuEvent)
             */
            @Override
            public void menuShown(MenuEvent e) {
                syncMenu();
            }
        });
    }
555748
function stylesheetOverride(stylesheet, props, themeData) {
  return {
    ...stylesheet,
    pointerBorder: { fill: themeData["tooltip.backgroundColor"] },
    pointerBody: { fill: themeData["tooltip.backgroundColor"] }
  };
}
1285078
private void fillMenu() {
        isBugItem = new MenuItem(menu, SWT.RADIO);
        isBugItem.setText("Bug");
        notBugItem = new MenuItem(menu, SWT.RADIO);
        notBugItem.setText("Not Bug");

        isBugItem.addSelectionListener(new SelectionAdapter() {
            /*
             * (non-Javadoc)
             *
             * @see
             * org.eclipse.swt.events.SelectionAdapter#widgetSelected(org.eclipse
             * .swt.events.SelectionEvent)
             */
            @Override
            public void widgetSelected(SelectionEvent e) {
                if (bugInstance != null) {
                    classifyWarning(bugInstance, true);
                }
            }
        });

        notBugItem.addSelectionListener(new SelectionAdapter() {
            /*
             * (non-Javadoc)
             *
             * @see
             * org.eclipse.swt.events.SelectionAdapter#widgetSelected(org.eclipse
             * .swt.events.SelectionEvent)
             */
            @Override
            public void widgetSelected(SelectionEvent e) {
                if (bugInstance != null) {
                    classifyWarning(bugInstance, false);
                }
            }
        });

        menu.addMenuListener(new MenuAdapter() {
            @Override
            public void menuShown(MenuEvent e) {
                // Before showing the menu, sync its contents
                // with the current BugInstance (if any)
                if (DEBUG) {
                    System.out.println("Synchronizing menu!");
                }
                syncMenu();
            }
        });
    }
961166
function( contentItem ) {
		if( this._maximisedItem !== null ) {
			this._$minimiseItem( this._maximisedItem );
		}
		this._maximisedItem = contentItem;
		contentItem.element.addClass( 'lm_maximised' );
		contentItem.element.after( this._maximisePlaceholder );
		this.container.prepend( contentItem.element );
		contentItem.element.width( this.container.width() );
		contentItem.element.height( this.container.height() );
		contentItem.callDownwards( 'setSize' );
	}
129510
function showMenu() {
        var self = this, menu = self.get('menu');    // does not put this into setter
                                                     // in case set menu before submenu item is  rendered
        // does not put this into setter
        // in case set menu before submenu item is  rendered
        var align = {
                node: this.$el,
                points: [
                    'tr',
                    'tl'
                ],
                overflow: {
                    adjustX: 1,
                    adjustY: 1
                }
            };
        util.mix(menu.get('align'), align, false);
        menu.show();
        self.el.setAttribute('aria-haspopup', menu.get('el').attr('id'));
    }
986378
private void addMenuItems(Menu mMenu, boolean subMenu) {
        int groupId = R.id.material_drawer_menu_default_group;
        for (int i = 0; i < mMenu.size(); i++) {
            MenuItem mMenuItem = mMenu.getItem(i);
            IDrawerItem iDrawerItem;
            if (!subMenu && mMenuItem.getGroupId() != groupId && mMenuItem.getGroupId() != 0) {
                groupId = mMenuItem.getGroupId();
                iDrawerItem = new DividerDrawerItem();
                getItemAdapter().add(iDrawerItem);
            }
            if (mMenuItem.hasSubMenu()) {
                iDrawerItem = new PrimaryDrawerItem()
                        .withName(mMenuItem.getTitle().toString())
                        .withIcon(mMenuItem.getIcon())
                        .withIdentifier(mMenuItem.getItemId())
                        .withEnabled(mMenuItem.isEnabled())
                        .withSelectable(false);
                getItemAdapter().add(iDrawerItem);
                addMenuItems(mMenuItem.getSubMenu(), true);
            } else if (mMenuItem.getGroupId() != 0 || subMenu) {
                iDrawerItem = new SecondaryDrawerItem()
                        .withName(mMenuItem.getTitle().toString())
                        .withIcon(mMenuItem.getIcon())
                        .withIdentifier(mMenuItem.getItemId())
                        .withEnabled(mMenuItem.isEnabled());
                getItemAdapter().add(iDrawerItem);
            } else {
                iDrawerItem = new PrimaryDrawerItem()
                        .withName(mMenuItem.getTitle().toString())
                        .withIcon(mMenuItem.getIcon())
                        .withIdentifier(mMenuItem.getItemId())
                        .withEnabled(mMenuItem.isEnabled());
                getItemAdapter().add(iDrawerItem);
            }
        }
    }
218044
def _showItemContextMenu(self, item, point, col):
        """"""
        menu = getattr(item, '_menu', None)
        if menu:
            settitle = getattr(item, '_set_menu_title', None)
            if settitle:
                settitle()
            # self._current_item tells callbacks what item the menu was referring to
            point = self.etw.mapToGlobal(point)
            self._current_item = item
            self.etw.clearSelection()
            self.etw.setItemSelected(item, True)
            menu.exec_(point)
        else:
            self._current_item = None
756080
private WMenu buildMenuBar(final WText selectedMenuText) {
		WMenu menu = new WMenu();

		// The Colours menu just shows simple text
		WSubMenu colourMenu = new WSubMenu("Colours");
		colourMenu.setMode(WSubMenu.MenuMode.LAZY);
		colourMenu.setAccessKey('C');
		addMenuItem(colourMenu, "Red", selectedMenuText);
		addMenuItem(colourMenu, "Green", selectedMenuText);
		addMenuItem(colourMenu, "Blue", selectedMenuText);
		colourMenu.addSeparator();
		colourMenu.add(new WMenuItem("Disable colour menu", new ToggleDisabledAction(colourMenu)));
		menu.add(colourMenu);

		// The Shapes menu shows grouping of items
		WSubMenu shapeMenu = new WSubMenu("Shapes");
		shapeMenu.setAccessKey('S');
		addMenuItem(shapeMenu, "Circle", selectedMenuText);

		WMenuItemGroup triangleGroup = new WMenuItemGroup("Triangles");
		shapeMenu.add(triangleGroup);
		shapeMenu.setMode(WSubMenu.MenuMode.DYNAMIC);
		addMenuItem(triangleGroup, "Equilateral", selectedMenuText);
		addMenuItem(triangleGroup, "Isosceles", selectedMenuText);
		addMenuItem(triangleGroup, "Scalene", selectedMenuText);
		addMenuItem(triangleGroup, "Right-angled", selectedMenuText);
		addMenuItem(triangleGroup, "Obtuse", selectedMenuText);

		WMenuItemGroup quadGroup = new WMenuItemGroup("Quadrilaterals");
		shapeMenu.add(quadGroup);
		addMenuItem(quadGroup, "Square", selectedMenuText);
		addMenuItem(quadGroup, "Rectangle", selectedMenuText);
		addMenuItem(quadGroup, "Rhombus", selectedMenuText);
		addMenuItem(quadGroup, "Trapezoid", selectedMenuText);
		addMenuItem(quadGroup, "Parallelogram", selectedMenuText);

		shapeMenu.addSeparator();
		shapeMenu.add(new WMenuItem("Disable shape menu", new ToggleDisabledAction(shapeMenu)));
		menu.add(shapeMenu);

		// The Image menu shows use of decorated labels and images
		WDecoratedLabel imageLabel = new WDecoratedLabel(new WImage("/image/wrench.png", "spanner"), new WText("Images"), null);
		WSubMenu imageMenu = new WSubMenu(imageLabel);
		imageMenu.add(createImageMenuItem("/image/flag.png", "Flag", "eg-menu-image-1",
				selectedMenuText));
		imageMenu.add(createImageMenuItem("/image/attachment.png", "Attachment", "eg-menu-image-2",
				selectedMenuText));
		imageMenu.add(createImageMenuItem("/image/settings.png", "Settings", "eg-menu-image-3",
				selectedMenuText));

		imageMenu.addSeparator();
		imageMenu.add(new WMenuItem("Disable image menu", new ToggleDisabledAction(imageMenu)));
		menu.add(imageMenu);

		WSubMenu sitesMenu = new WSubMenu("External apps");
		sitesMenu.add(new WMenuItem("External website", "http://www.example.com/"));
		WMenuItem google = new WMenuItem("Example (new window)", "http://www.example.com/");
		google.setTargetWindow("exampleWindow");
		sitesMenu.add(google);
		menu.add(sitesMenu);

		// Add an item to toggle the states of all the menus
		menu.add(new WMenuItem("Toggle top-level menus", new ToggleDisabledAction(colourMenu,
				shapeMenu, imageMenu,
				sitesMenu)));

		menu.add(new WMenuItem("Link", "http://www.example.com"));
		menu.add(new WMenuItem("No Action"));

		WMenuItem itemWithIcon = new WMenuItem("Help");
		itemWithIcon.setAction(new Action() {
			@Override
			public void execute(final ActionEvent event) {
				// do something
			}
		});
		itemWithIcon.setHtmlClass(HtmlClassProperties.ICON_HELP_BEFORE);
		menu.add(itemWithIcon);

		WMenuItem itemWithImage = new WMenuItem(new WDecoratedLabel(new WImage("/image/home.png", "home"), new WText("Home"), null));
		menu.add(itemWithImage);
		menu.add(new WMenuItem(new WDecoratedLabel(new WImage("/image/settings.png", "settings"), new WText("Settings Menu"), null)));
		itemWithImage = new WMenuItem(new WDecoratedLabel(new WImage("/image/flag.png", "flag")));
		itemWithImage.setAccessibleText("flag this view");
		menu.add(itemWithImage);
		return menu;
	}
448792
private void initComponents() {

        popMenu = new javax.swing.JPopupMenu();
        menuDelete = new javax.swing.JMenuItem();
        pnlAddProperty = new javax.swing.JPanel();
        cmdAdd = new javax.swing.JButton();
        pnlPropertyMapping = new javax.swing.JPanel();
        scrPropertyList = new javax.swing.JScrollPane();
        lstProperties = new javax.swing.JTable();
        lblCurrentPropertyMapping = new javax.swing.JLabel();

        menuDelete.setText("Delete mapping");
        menuDelete.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                menuDeleteActionPerformed(evt);
            }
        });
        popMenu.add(menuDelete);

        setAlignmentX(5.0F);
        setAlignmentY(5.0F);
        setFont(new java.awt.Font("Arial", 0, 18)); // NOI18N
        setMinimumSize(new java.awt.Dimension(280, 500));
        setPreferredSize(new java.awt.Dimension(280, 500));
        setLayout(new java.awt.BorderLayout());

        pnlAddProperty.setBorder(javax.swing.BorderFactory.createEmptyBorder(0, 0, 3, 0));
        pnlAddProperty.setLayout(new java.awt.BorderLayout(3, 0));
        Vector<Object> v = new Vector<Object>();
        for (IRI dp : obdaModel.getCurrentVocabulary().dataProperties()) {
            v.addElement(new PredicateItem(dp, PredicateItem.PredicateType.DATA_PROPERTY, prefixManager));
        }
        for (IRI op : obdaModel.getCurrentVocabulary().objectProperties()) {
            v.addElement(new PredicateItem(op, PredicateItem.PredicateType.OBJECT_PROPERTY, prefixManager));
        }
        cboPropertyAutoSuggest = new AutoSuggestComboBox(v);
        cboPropertyAutoSuggest.setRenderer(new PropertyListCellRenderer());
        cboPropertyAutoSuggest.setMinimumSize(new java.awt.Dimension(195, 23));
        cboPropertyAutoSuggest.setPreferredSize(new java.awt.Dimension(195, 23));
        JTextField txtComboBoxEditor = (JTextField) cboPropertyAutoSuggest.getEditor().getEditorComponent();
        txtComboBoxEditor.addKeyListener(new java.awt.event.KeyAdapter() {
            public void keyPressed(java.awt.event.KeyEvent evt) {
                cboPropertyAutoSuggestKeyPressed(evt);
            }
        });
        pnlAddProperty.add(cboPropertyAutoSuggest);

        cmdAdd.setBorder(javax.swing.BorderFactory.createEtchedBorder());
        cmdAdd.setContentAreaFilled(false);
        cmdAdd.setFocusable(false);
        cmdAdd.setMaximumSize(new java.awt.Dimension(23, 23));
        cmdAdd.setMinimumSize(new java.awt.Dimension(23, 23));
        cmdAdd.setPreferredSize(new java.awt.Dimension(23, 23));
        cmdAdd.setIcon(IconLoader.getImageIcon("images/plus.png"));
        cmdAdd.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                cmdAddActionPerformed(evt);
            }
        });
        pnlAddProperty.add(cmdAdd, java.awt.BorderLayout.EAST);

        add(pnlAddProperty, java.awt.BorderLayout.PAGE_START);

        pnlPropertyMapping.setLayout(new java.awt.BorderLayout());

        lstProperties.setModel(new DefaultTableModel(0, 1));
        lstProperties.setCellSelectionEnabled(true);
        lstProperties.setRowHeight(65);
        lstProperties.setSelectionMode(javax.swing.ListSelectionModel.SINGLE_SELECTION);
        lstProperties.setTableHeader(null);
        lstProperties.addMouseListener(new java.awt.event.MouseAdapter() {
            public void mousePressed(java.awt.event.MouseEvent evt) {
                lstPropertiesMousePressed(evt);
            }
            public void mouseReleased(java.awt.event.MouseEvent evt) {
                lstPropertiesMouseReleased(evt);
            }
        });
        lstProperties.addKeyListener(new java.awt.event.KeyAdapter() {
            public void keyPressed(java.awt.event.KeyEvent evt) {
                lstPropertiesKeyPressed(evt);
            }
        });
        new EditableCellFocusAction(lstProperties, KeyStroke.getKeyStroke(KeyEvent.VK_ENTER, 0));
        new EditableCellFocusAction(lstProperties, KeyStroke.getKeyStroke(KeyEvent.VK_F2, 0));
        scrPropertyList.setViewportView(lstProperties);

        pnlPropertyMapping.add(scrPropertyList, java.awt.BorderLayout.CENTER);

        lblCurrentPropertyMapping.setFont(new java.awt.Font("Tahoma", 1, 12)); // NOI18N
        lblCurrentPropertyMapping.setForeground(new java.awt.Color(53, 113, 163));
        lblCurrentPropertyMapping.setText("Current property mappings:");
        lblCurrentPropertyMapping.setBorder(javax.swing.BorderFactory.createEmptyBorder(2, 2, 2, 2));
        pnlPropertyMapping.add(lblCurrentPropertyMapping, java.awt.BorderLayout.NORTH);

        add(pnlPropertyMapping, java.awt.BorderLayout.CENTER);
    }
442371
function Menu() {
  ui.Emitter.call(this);
  this.items = {};
  this.el = $(html).hide().appendTo('body');
  this.el.hover(this.deselect.bind(this));
  $('html').click(this.hide.bind(this));
  this.on('show', this.bindKeyboardEvents.bind(this));
  this.on('hide', this.unbindKeyboardEvents.bind(this));
}
1121935
private void createSubMenu(
        CmsContextMenuItemWidget parentWidget,
        ContextMenuItemState childState,
        CmsContextMenuConnector connector) {

        CmsContextMenuItemWidget childWidget = createEmptyItemWidget(
            childState.getId(),
            childState.getCaption(),
            childState.getDescription(),
            connector);
        childWidget.setEnabled(childState.isEnabled());
        childWidget.setSeparatorVisible(childState.isSeparator());
        setStyleNames(childWidget, childState.getStyles());
        parentWidget.addSubMenuItem(childWidget);

        for (ContextMenuItemState child : childState.getChildren()) {
            createSubMenu(childWidget, child, connector);
        }
    }
867290
function () {
        var self = this;

        function activateMenuItemsByValue(menu, value) {
          if (menu instanceof Menu) {
            menu.items().each(function (ctrl) {
              if (!ctrl.hasMenus()) {
                ctrl.active(ctrl.value() === value);
              }
            });
          }
        }

        function getSelectedItem(menuValues, value) {
          var selectedItem;

          if (!menuValues) {
            return;
          }

          for (var i = 0; i < menuValues.length; i++) {
            if (menuValues[i].value === value) {
              return menuValues[i];
            }

            if (menuValues[i].menu) {
              selectedItem = getSelectedItem(menuValues[i].menu, value);
              if (selectedItem) {
                return selectedItem;
              }
            }
          }
        }

        self.on('show', function (e) {
          activateMenuItemsByValue(e.control, self.value());
        });

        self.state.on('change:value', function (e) {
          var selectedItem = getSelectedItem(self.state.get('menu'), e.value);

          if (selectedItem) {
            self.text(selectedItem.text);
          } else {
            self.text(self.settings.text);
          }
        });

        return self._super();
      }