used for easy debugging and while working on Responsive web layout

RWD

body {
  background-color: red;
}

@media only screen and (min-width: 544px) {
  body {
    background-color: blue;
  }
}

@media only screen and (min-width: 768px) {
  body {
    background-color: green;
  }
}

@media only screen and (min-width: 992px) {
  body {
    background-color: yellow;
  }
}

@media only screen and (min-width: 1200px) {
  body {
    background-color: orange;
  }
}