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

		Color innerHighlight = c.getBackground().brighter();
		Color outerHighlight = innerHighlight.brighter();
		Color innerShadow = c.getBackground().darker();
		Color outerShadow = innerShadow.darker();

		// upper
		g.setColor(outerHighlight);
		g.drawLine(1, offset, w - 3, offset); 	// upper outer
		g.setColor(innerHighlight);
		g.drawLine(2, offset + 1, w - 3, offset + 1); 	// upper inner

		// left
		g.setColor(outerShadow);
		g.drawLine(0, offset + 1, 0, h - 1); 		// left outer
		g.setColor(innerHighlight);
		g.drawLine(1, offset + 1, 1, h - 2); 		// left inner

		// right
		g.setColor(innerShadow);
		g.drawLine(w - 2, offset + 1, w - 2, h); // right inner
		g.setColor(outerShadow);
		g.drawLine(w - 1, offset + 1, w - 1, h - 2); // right outer

		if (!selected) {
			g.setColor(outerHighlight);
			g.drawLine(0, h - 1, w - 1, h - 1);	// bottom
		}

		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/GTabBorder.java