JSFiddle - React, Tailwind, and code Playground

HTML

<div id="masthead"></div>

CSS

@keyframes slideleft {
    from {
        background-position: 0%;
    }
    
    to {
        background-position: 90000%;
    }
}

@-webkit-keyframes slideleft {
    from {
        background-position: 0%;
    }
    to {
        background-position: 90000%;
    }
}

#masthead {
    background-image: url('http://static.communitytable.parade.com/wp-content/uploads/2014/06/dogs-in-world-cup-jerseys-ftr.jpg');
    background-repeat: repeat-x;
    animation: slideleft 600s infinite linear;
    -webkit-animation: slideleft 600s infinite linear;
    width: 100%;
    height: 1200px;
}