// styleswitch.php
$style = $_GET['style'];

if(!is_numeric($style)) {
die();
}

$value = null;
switch($style) {
	case '1':
	$value = "default.css";
	break;
	case '2':
	$value = "darksky.css";
	break;
	case '3':
	$value = "halext.css";
	break;
	case '4':
	$value = "flashii.css";
	break;
	case '5':
	$value = "zeniea.css";
	break;
	default:
	$value = "default.css";
	break;
	}

	setcookie("blogStyle", $value, time() + 315569260);
	header('Location: ' . $_SERVER['HTTP_REFERER']);

// This goes in the webpage
<link rel="stylesheet" type="text/css" href="css/<?php if(!isset($_COOKIE["blogStyle"])) { echo 'default.css'; } else { echo $_COOKIE['blogStyle']; } ?>" />

<li>Style Switcher: </li>
<li><a href="styleswitch.php?style=1">Default</a></li>
<li><a href="styleswitch.php?style=2">Darksky</a></li>
<li><a href="styleswitch.php?style=3">Halext</a></li>
<li><a href="styleswitch.php?style=4">Flashii</a></li>
<li><a href="styleswitch.php?style=5">Zeniea</a></li>