:root {
  background-image: url(/images/contour_bleu_vert_top_left.gif);
  background-repeat: no-repeat;
  background-attachment: fixed;
  background-position: left top;
  
  background-image: url(/images/contour_bleu_vert_bottom_right.gif);
  background-repeat: no-repeat;
  background-attachment: fixed;
  background-position: left top;
}