@media screen and (min-width:500px) {
  .fixed-box-right {
    margin-left: 52%;
  }
  blockquote .fixed-box-right {
    margin-left: 52%;
  }
  .fixed-box-center {
    margin-left: 20%;
    margin-right: 20%;
  }
  blockquote .fixed-box-center {
    margin-left: 14%;
    margin-right: 14%;
  }
}