$re = '/<style[^>]*>([^<]+)?<[\s\/]+style>/m';
$str = '<head>
<meta property="og:locale" content="en_US" />
<meta property="og:type" content="website" />
<style>html{line-height:1.15;-ms-text-size-adjust:100%;-webkit-text-size-adjust:100%;}</style>
<link rel=\'dns-prefetch\' href=\'//js.stripe.com\' />
<style id="pf-used-css">button,hr,input{overflow:visible;}[type="checkbox"],[type="radio"],legend{box-sizing:border-box;padding:0;}html{line-height:1.15;-ms-text-size-adjust:100%;-webkit-text-size-adjust:100%;}body,h1,h2,h3,h4,h5,h6{margin:0;}article,aside,details,figcaption,figure,footer,header,main,menu,nav,section{display:block;}hr{background-image:url("data:image/svg+xml;charset=utf-8,<svg viewBox=\\"0 0 50 50\\" height=\\"24\\" width=\\"24\\" xmlns=\\"http://www.w3.org/2000/svg\\" fill=\\"%23B0B0B0\\"><path d=\\"M 9.15625 6.3125 L 6.3125 9.15625 L 22.15625 25 L 6.21875 40.96875 L 9.03125 43.78125 L 25 27.84375 L 40.9375 43.78125 L 43.78125 40.9375 L 27.84375 25 L 43.6875 9.15625 L 40.84375 6.3125 L 25 22.15625 L 9.15625 6.3125 z\\"/></svg>");}.swal-label-required{display:inline-block;position:relative;right:9999px;margin-left:10px;}</style>
<style>html{line-height:1.15;-ms-text-size-adjust:100%;-webkit-text-size-adjust:100%;}</style>
</head>
<body>';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php