ADD THIS TO THE PAGE HEADER CODE INJECTION FOR THE BLOG.
<style>
.Header.Header--bottom {background-image: url('//static1.squarespace.com/static/59e00594d55b41c2c7c2cf78/t/59e6a14564b05f6bc9855313/1508286789602/footer5.jpg'); background-size: cover; background-position: center; padding-bottom: 30px;}
.Header-nav-item {color: white!important;}
</style>