nur zu fragen... have meine header Tag , gut gemach ?
<?php
header('Content-Type: text/html; Charset=utf-8');
mb_internal_encoding('UTF-8');
date_default_timezone_set('UTC');
error_reporting(E_ALL);
?>
<!doctype html>
<html lang="en">
<head>
<meta name="viewport" content="width=device-width, initial-scale=1">
<meta http-equiv="content-type" content="text/html; charset=utf-8">
<title>Computer</title>
<link rel="stylesheet" href="CSS/windows.css">
<link rel="stylesheet" href="CSS/tablet.css">
</head>
<header>
<picture class="bilder">
<source media='(min-width: 320px) and (max-width: 568px) and (orientation: portrait)' srcset='/Bilder/night_hoppe.JPG'/>
<source media='(max-width: 768px) and (orientation: landscape)' srcset='/Bilder/night_smartphone.JPG'/>
<source media='(min-width: 1280px)' srcset='/Bilder/night.JPG'/>
<img src='night_smartphone.JPG' alt='night'>
</picture>
</header>
<body>