IonRutz

First add the CSS to Dashboard > Appearances > Editor > Style.css, preferably after all the content:

#toTop {position:fixed;bottom:5px;right:5px;cursor:pointer; z-index: 99;}



Then, inside the same Dashboard > Appearances > Editor choose Footer.php in the right files and drop this code code before the </html> tag:

<img src="http://cursowebdesign.com/assets/img/to-top.png" id="toTop" alt="Back to top">
<script>