1. body {
    2.   width: 100%;
    3.   margin: 0 auto;
    4.   min-width: 320px;
    5.   max-width: 640px;
    6.   background: #fff;
    7.   font-size: 14px;
    8.   font-family: -apple-system, Helvetica, sans-serif;
    9.   line-height: 1.5;
    10.   color: #666;
    11. }