middle moblie content

by John Doe

HTML

<div class="content">
<div class="container">
<div class="box"><a><img src="http://placehold.it/300x300?text=img"></a></div>
<div class="box"><a><img src="http://placehold.it/300x300?text=img"></a></div>
<div class="box"><a><img src="http://placehold.it/300x300?text=img"></a></div>
<div class="box"><a><img src="http://placehold.it/300x300?text=img"></a></div>
<div class="box"><a><img src="http://placehold.it/300x300?text=img"></a></div>
<div class="box"><a><img src="http://placehold.it/300x300?text=img"></a></div>
<div class="box"><a><img src="http://placehold.it/300x300?text=img"></a></div>
<div class="box"><a><img src="http://placehold.it/300x300?text=img"></a></div>
<div class="box"><a><img src="http://placehold.it/300x300?text=img"></a></div>
</div>
</div>
<div class="footer"></div>

CSS

body{
  margin:0;
  position: relative;
  background-color: #ffffff;}
.content{
  display:flex;
  justify-content:center;align-items:center;width:500px;
  height: 100%;
  background-color: red;
}
.container{
  display: inline-block;
  width: 300px;
  margin: 0 auto;
  vertical-align: middle;
}
.box{
  width: 33.333%;
  height: auto;
  position: relative;
  float: left;
  padding: 0 10px;
  box-sizing: padding-box;
  margin-bottom: 10px;
}
a{
  display: block;
  padding: 10px;
  border: 1px solid #0C75B0;
  border-radius: 4px;
}
img{
  width: 100%;
  height: auto;
}

.footer{
  position: fixed;
  bottom: 0px;
  height: 40px;
  width: 100%;
  background-color: #0876BA;
  display: block;
}