@media screen and (max-width: 900px) {
  body {
    padding: 5px;
  }
  #wrapper,
  #header,
  #logo,
  #leftcolumn,
  #boxnavi,
  #boxblau,
  #contentcolumn,  
  #rightcolumn,
  #textboxlonglefttopimag,
  #textboxsquaremidtop,
  #textboxlongleftbottom ,
  #textboxlonglefttop
  {
    width: 100%;
  }
  
  #topimpressum,
  #topimpressumkasten,
  #topimpressumkastenshort
   {
    width: 100%;
    float: none;
  }
  #textboxlonglefttopimag img {
	  max-width: 100%;
	  height: 100%;
  }
  #textboxsquareleftbottomimag img {
	  max-width: 100%;
	  height: 100%;
}
  #textboxsquarerighttopimag img {
	  max-width: 100%;
	  height: 100%;
}