styles.css

body {
   margin: 0 auto;
   max-width: 1000px;
   background: url('assets/img/sandbox.png') no-repeat center;
   display: flex;
   flex-direction: column;
   height: 100%;
   font-family: 'Source Sans Pro', calibri, Arial, sans-serif !important;
   min-height: 550px;
}
.content {
   flex: 1 0 auto;
}
footer {
   padding: 10px 0;
   text-align: center;
}