add <img style=“width: 100%; position: absolute; top: 50%; left: 0;” src=“https://64.media.tumblr.com/71a729c07330539e046eca9cf3006205/cdedacdbc41c5bb0-a5/s400x600/523aa624bbd3f515b490040782344f94f7f4a4cd.gif”/> right after the <body> tag in your blog’s html
