body {
  font-family: helvetica, arial, 'hiragino kaku gothic pro', meiryo, 'ms pgothic', sans-serif;
}
@media screen and (max-width: 900px) {
 img {
      max-width:100%;
      height: auto;
     }

.contents{
    padding: 1px;
    width:100%
    max-width: 900px;
    }
 .no_display {
      display : none;
     }
}
@media screen and (min-width: 901px) {
.contents{
    position: absolute;
    left: 50%;
    width:100%
    max-width: 900px;
    margin-left: -450px;
    margin-right: 300px;
  }
.display {
      display : none;
     }
}