*, *::before, *::after {
  box-sizing: border-box;
}

 .cf::before,
 .cf::after  {
    content: "";
    display: block; 
  }
  .cf::after {
  clear: both;  
  }
  .cf {
  zoom: 1; /* for old ie (trigger has layout) */  
  }

  body {
    width: 100%;
  }

  img {
    max-width: 100%;
    margin-top: 25%;
  }