body { font-family: sans-serif; padding: 20px; max-width: 600px; margin: auto; }
.cupon { position: relative; width: 100%; max-width: 500px; }
.cupon img { width: 100%; }
.texto {
  position: absolute;
  color: yellow;
  font-family: 'Arial', sans-serif;
  font-weight: bold;
}
.neon {
  font-size: 3em;
  text-shadow: 0 0 8px rgba(255,255,0,0.7);
}

#txt-cliente { top: 43%; left: 26%; }
#txt-descuento { top: 44%; right: 10%; }
#txt-fecha-gen { top: 48%; left: 39%; }
#txt-fecha-venc { top: 52.5%; left: 39.5%; }
#txt-numero { top: 60%; left: 27.5%; }