div{
    width: 90%;
    height: 100px;
    margin: 20px auto;
    padding: 40px;
    border: 2px solid black;
    box-sizing: border-box;
    background-color: orange;
}
.d1,.d2,.d3{
  transition-property: background-color;
}
.d1{
  transition-duration: 2s;
}
.d2{
  transition-duration: 4s;
}
.d3{
  transition-duration: 8s;
}
.d1:hover,.d2:hover, .d3:hover{
    background-color: blue;
}