function tabnav(t){
	document.getElementById('why').style.display="none";
	document.getElementById('what').style.display="none";
	document.getElementById('properties').style.display="none";
	document.getElementById('TopSEOreactions').style.display="none";
	
	document.getElementById('lwhy').style.background="none";
	document.getElementById('lwhat').style.background="none";
	document.getElementById('lproperties').style.background="none";
	document.getElementById('lblog').style.background="none";
	
	if (t == 'why'){
	    document.getElementById('why').style.display="";
	    document.getElementById('lwhy').style.background="#fff";
	}
	if (t == 'what'){
	    document.getElementById('what').style.display="";
	    document.getElementById('lwhat').style.background="#fff";
	}
	if (t == 'properties'){
	    document.getElementById('properties').style.display="";
	    document.getElementById('lproperties').style.background="#fff";
	}
	if (t == 'TopSEOreactions'){
	    document.getElementById('TopSEOreactions').style.display="";
	    document.getElementById('lblog').style.background="#fff";
	}
}