var styles = ["80%", "100%" , "110%" , "120%" , "130%" , "140%" ]
    var style = 2
    function changestyle(l_direction)
        {
        if ( ( style > 1 ) && ( l_direction == -1 ) ) { style -- }
        if ( ( style < 6 ) && ( l_direction == 1 ) ) { style ++ }
        document.getElementById("contenu").style.fontSize = styles[style-1]
        }