@Override
	public void paintBorder(Component c, Graphics g, int x, int y, int w, int h) {
		Insets insets = getBorderInsets(c);
		Color oldColor = g.getColor();
		g.translate(x, y);

		Color highlight = GTab.TAB_BG_COLOR.brighter().brighter();

		g.setColor(GTab.SELECTED_TAB_BG_COLOR);
		g.fillRect(insets.left, h - insets.bottom, w - insets.right - 1, insets.bottom);

		g.setColor(highlight);
		g.drawLine(insets.left, h - insets.bottom - 1, w - insets.right - 1, h - insets.bottom - 1);

		g.translate(-x, -y);
		g.setColor(oldColor);
	}
Paints the border, and also a bottom shadow border that isn't part of the insets, so that
the area that doesn't have tabs, still paints a bottom border
Ghidra/Framework/Docking/src/main/java/docking/widgets/tab/GTabPanelBorder.java