body {
  background: white;    
}

/*@media screen and (min-width: 600px)  {
  body {
    
    background: red;
  }
}*/

@media screen  and (min-width: 600px) /* Tablet */ {
  body {
    /*background: blue;*/
    /*background-image: url("a.jpg");*/

  }

  .one{
    width: 100%;
  }
}

@media screen and (max-width: 599px) /* Mobile */ {
  body {
    /*background: green;*/
  }

  .one{
    width: 100%;
    /*height: 20%;*/
  }
}