Bug 283631 [CSS] ETabFolder in CTabFolder mode top/bottom keylines differ
bundles/org.eclipse.e4.ui.widgets/src/org/eclipse/e4/ui/widgets/ETabFolder.java
int y2 = onBottom ? size.y - tabHeight - borderBottom - 1 : size.y - borderBottom;
		gc.drawLine(x1, y1, x1, y2); 
		gc.drawLine(x2, y1, x2, y2); 
		if (onBottom) {
			gc.drawLine(x1, y1, x2, y1); 
		} else {
			gc.drawLine(x1, y2, x2, y2); 
		}
	}
}
void drawTabArea(Event event) {
	if (!webbyStyle || onBottom || single) {
		super.drawTabArea(event);
		return;
	}
	GC gc = event.gc;
	Point size = getSize();
	int[] shape = null;
	Color borderColor = exteriorKeyLineColor;
	if (tabHeight == 0) {
		int style = getStyle();
		if ((style & SWT.FLAT) != 0 && (style & SWT.BORDER) == 0)
			return;
		int x1 = borderLeft - 1;
		int x2 = size.x - borderRight;
		int y1 = borderTop + highlight_header;
		int y2 = borderTop;
		if (borderLeft > 0 && onBottom)
			y2 -= 1;
		shape = new int[] { x1, y1, x1, y2, x2, y2, x2, y1 };