@media only screen and (max-width: 767px) {
  /* CSS rules for phones go here */

  html {
    font-size: 45%;
  }
}

@media only screen and (max-width: 767px) {
  /* CSS rules for phones go here */

  html {
    font-size: 45%;
  }
}

@media only screen and (min-device-width: 920px) and (max-device-width: 3780px) {
  /* Styles */

  header {
    margin: 10% auto;
    width: 60%;
    text-align: center;
  }
}

@media only screen and (min-device-width: 1900px) and (max-device-width: 7780px) {
  /* Styles */

  header {
    margin: 10% auto;
    width: 40%;
    text-align: center;
  }
}