.example_mbr {
  background-color: red;
  width: 300px;
  height: 300px;
}
@media only screen and (max-width: 1920px) {
  .example_mbr {
    width: 300px;
    height: 300px;
    background-color: red;
  }
}
@media only screen and (max-width: 980px) {
  .example_mbr {
    width: 200px;
    height: 200px;
    background-color: blue;
  }
}
@media only screen and (max-width: 640px) {
  .example_mbr {
    width: 100px;
    height: 100px;
    background-color: green;
  }
}