#header
{
  background: url(../css_images/h_tipp.jpg) no-repeat;
}

#Montag #header
{
  background: url(../css_images/header_tipp_Mo.jpg) no-repeat;
}

#Donnerstag #header
{
  background: url(../css_images/header_tipp_Do.jpg) no-repeat;
}

#Mittwoch #header
{
  background: url(../css_images/h_tipp.jpg) no-repeat;
}