propagation.css

div {
  position: absolute;
  border: none;
}
div:hover {
  background: green !important;
}
#div1 {
  top: 0;
  left: 0;
  width: 300px;
  height: 300px;
  background: blue;
}
#div2 {
  top: 75px;
  left: 75px;
  width: 150px;
  height: 150px;
  background: red;
}