JComponent (@NotNull JRootPane rootPane, @NotNull JComponent northComponent) { if (isVersion2()) { return MacWinTabsHandlerV2._wrapRootPaneNorthSide(rootPane, northComponent); } JPanel panel = new NonOpaquePanel(new BorderLayout()); JPanel filler = new OpaquePanel(); filler.setBorder(JBUI.Borders.customLineBottom(UIUtil.getTooltipSeparatorColor())); filler.setVisible(false); panel.add(filler, BorderLayout.NORTH); panel.add(northComponent); rootPane.putClientProperty(WIN_TAB_FILLER, filler); rootPane.putClientProperty("Window.transparentTitleBarHeight", 28); return panel; }