body {
   background-color: white;
   color: black;

   @media only screen and (max-width: 500px) {
.box {
   background-color: #333;
   font-family: 'Source Sans Pro', Tahoma;
   font-size:18px;
   font-weight:600;
   color:#fff;
   width:100%;
   margin:0 auto;
   margin-top:100px
}
.box-pad {
   padding:20px
}

}

@media only screen and (min-width: 100px) {
.box-pad {
   padding:0
}
.box {
   background-color: #333;
   font-family: 'Source Sans Pro', Tahoma;
   font-size:18px;
   font-weight:600;
   color:#fff;
   padding:20px;
   width:900px;
   margin:0 auto;
   margin-top:100px
}

}

body {
   padding:0;
   margin:0
}
}