body {
  width: 50em;
  margin: 1em auto;
  border: 1px solid black;
}

.ylatunniste {
  margin: 0;
  border-bottom: 1px solid black;
  padding: 0.5em 1em;
  background-color: #FFFF99;
}

.vasennavi {
  width: 6em;
  background-color: #99CCFF;
  float: left;
  padding: 1em;
}

.oikeanavi {
  width: 6em;
  background-color: #FF99CC; 
  float: right;
  padding: 1em;
}

.sisalto {
  border-left: 8em solid #99CCFF;
  border-right: 8em solid #FF99CC;
  padding: 1em;
}

.sisalto:after {
  content: '';
  clear: both;
  display: block;
  height: 0;
}

.alatunniste {
  border-top: 1px solid black;
  padding: 0.5em 1em;
  background-color: #66FF99;
}