Cookies Warning Front

<?php
session_start();
?>

<html>
<head>
    <style>
    .cookies {
        opacity:0.8;
        position: fixed;
        bottom: 0;
        left: 0px;
        width: 100%;
        background-color: #24578e;
        padding:10px;
        font-size:12px;
        text-align:center;
        color:#fff;
    }
    .cookies.off{visibility:hidden;}
    .cookies input{float:right;margin-right:20px;width:auto;}
    </style>
</head>
<body>
<p>some<br>very<br>long<br>text<br>some<br>very<br>long<br>text<br>some<br>very<br>long<br>text<br>some<br>very<br>long<br>text<br>some<br>very<br>long<br>text<br>some<br>very<br>long<br>text<br>some<br>very<br>long<br>text<br>some<br>very<br>long<br>text<br>some<br>very<br>long<br>text<br></p>
<script>
function CookieClose(){
    var x = document.getElementById("CookieWarning");
    x.className += " off";
    var xhttp;
    xhttp = new XMLHttpRequest();
    xhttp.open("GET", "/helpers/set_cookies_off.php", true);
    xhttp.send();
}
</script>

<?php if(!isset($_SESSION['cookie'])){#hide if already closed! ?>
    <div class="cookies" id="CookieWarning">
            Cookies warning text!  <input type="button" value="Close" onclick="CookieClose()">
    </div>
<?php } ?>
</body>
</html>