mobile layout not implemented notification message (for sites in development)

mobile_not_implemented.css

/* mobile
============================================================================================== */
@media screen and (min-width: 0) and (max-width: 700px) {
  /* hide everything */
  div, span, p
  {
    display: none;
  }

  body:before {   
    background: #ffc;   
    width: 96%;   
    padding: 1em 2%;   
    float: left;   
    clear: both;   
    font-size: 14px;   
    font-size: .875rem;      

    content: "Mobile layout not implemented";
  } 
}