body{
    background-color: rgb(169, 229, 240);
}
ul {
  list-style-type: none;
  margin: 0;
  padding: 0;
  width: 25%;
  background-color: #f1f1f1;
  height: 100%; 
  position: fixed; 
  overflow: auto; 
}
li a {
  display: block;
  
  font-family: 'Lucida Sans';
  text-decoration: none;
  color: black;
  padding: 8px 16px;
   border-bottom: 1px solid black;
}
li a:hover:not(.active) {
  background-color: #555;
  color: white;
}

li a.active {
  background-color: #0439aa;
  color: white;
}

div{
    margin-left:25%;padding:1px 16px;height:1000px;
}