@keyframes target-hint {
  from {
    box-shadow: 0 0 .5em .2em #36c;
  }
  to {
    box-shadow: none;
  }
}

#SeitenKoordinaten:target {
   box-shadow: 0 0 .5em .2em #36c;
   animation: target-hint 1s linear 2s 1 forwards;
}