SOURCE

/* for 1080+ px width screen */

@media only screen and (min-width: 1080px) {
  html,
  body {
    font-size: 51.67px;
  }
}

/* for 1080 px width screen */

@media only screen and (max-width: 1080px) {
  html,
  body {
    font-size: 43px;
  }
}

/* for 800 px width screen */

@media only screen and (max-width: 800px) {
  html,
  body {
    font-size: 33px;
  }
}

/* for 720 px width screen */

@media only screen and (max-width: 720px) {
  html,
  body {
    font-size: 30px;
  }
}

/* for 640 px width screen */

@media only screen and (max-width: 640px) {
  html,
  body {
    font-size: 27px;
  }
}

/* for 540 px width screen */

@media only screen and (max-width: 540px) {
  html,
  body {
    font-size: 22.5px;
  }
}

/* for 480 px width screen */

@media only screen and (max-width: 480px) {
  html,
  body {
    font-size: 20px;
  }
}

/* for 450 px width screen */

@media only screen and (max-width: 450px) {
  html,
  body {
    font-size: 18.9px;
  }
}

/* for 414 px width screen */

@media only screen and (max-width: 414px) {
  html,
  body {
    font-size: 17.25px;
  }
}

/* for 375 px width screen */

@media only screen and (max-width: 375px) {
  html,
  body {
    font-size: 15.625px;
  }
}

/* for 320 px width screen */

@media only screen and (max-width: 320px) {
  html,
  body {
    font-size: 13.5px;
  }
}