This is my code, I want to show hover effect on after element.
 #car:after:hover{background:red:}
but this is not working.
This is my code, I want to show hover effect on after element.
 #car:after:hover{background:red:}
but this is not working.
 
    
    check out this demo below. I think you are missing content property. 
the Red div is created using :after and changes its color on hover.
the selector:after:hover won't work.
.car {
  position: relative;
  width: 100px;
  height: 100px;
  background: yellow;
}
.car:hover {
  background: skyblue;
}
.car:after {
  content: '';
  width: 50px;
  height: 50px;
  position: absolute;
  right: 0;
  bottom: 0;
  background: green;
}
.car:hover:after {
  background: red;
}<div class="car"></div>