css
/* styles for desktop devices */
@media only screen and (min-width: 992px) {
  body {
    font-size: 16px;
    width: 80%;
    margin: auto;
  }
}

/* styles for tablet devices */
@media only screen and (min-width: 768px) and (max-width: 991px) {
  body {
    font-size: 14px;
    width: 90%;
    margin: auto;
  }
}

/* styles for mobile devices */
@media only screen and (max-width: 767px) {
  body {
    font-size: 12px;
    width: 100%;
    margin: 0;
  }
}