Quick way to add leave site button on WordPress

functions.php

/* Add to the bottom of the page */

<?php

	function addHideSiteButton() {
?>
<div id="hide-site">
    <button onclick="hideSite()">Leave this site</button>
</div>

<script>
    function hideSite() {
        window.open("http://www.comicrelief.com/", "_newtab");
        location.replace("http://www.google.co.uk")
    }
</script>
<?php
	}
	add_action('theme_after_body_tag_start','addHideSiteButton')

?>

style.css

/* I recommend putting this in the Theme >> Customize >> Additonal CSS section */
/* ------
Hide Site 
------ */
div#hide-site {
    position: fixed;
    right: 10%;
    top: 90px;
    z-index: 1000;
}
div#hide-site button {
    background: #fbe697;
    color: #3b4248;
    border: 2px solid #2bb1a8;
    box-shadow: none;
    font-weight: bold;
    padding: 0.8em;
    text-transform: uppercase;
    transition: all 0.2s ease;
}
div#hide-site button:hover {
    background: #FAAE3D;
}
@media screen and (max-width: 1139px) { 
    div#hide-site {
        top: 0;
        right: 10%;
    }
}