Magento 1 critical CSS

readme.md

demo.php contains a code snippet that should be inserted into head.phtml to make it work within Magento 1. Don't forget to change the demo file_get_contents call by the actual $this->getCssJsHtml() call and set the right path as $skin_url.

CSS is for demo purposes only, use your own determined critical CSS by following my guide: CSS critical path in Magento 1.

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critical-all.css

.no-critical-pos,
.no-critical {
	opacity: 0!important;
	transition: opacity 0.1s ease-in;
}
.no-critical-pos {
	position: absolute!important;
}

* {
    outline: none!important;
}
*, ::after, ::before {
    box-sizing: inherit;
}
.clearer:after {
    display: block;
    content: ".";
    clear: both;
    font-size: 0;
    line-height: 0;
    height: 0;
    overflow: hidden;
}

html {
    -webkit-text-size-adjust: 100%;
    -ms-text-size-adjust: 100%;
    text-size-adjust: 100%;
}
html {
    box-sizing: border-box;
    -ms-overflow-style: scrollbar;
}

html, body {
    background-color: #fff;
    font: 13px/1 'Roboto', sans-serif;
    color: #2d2d2d;
    text-align: center;
    margin: 0;
}

a {
    color: #2d2d2d;
	text-decoration: none;
}

.fa {
	min-width: 10px;
    display: inline-block;
    font-style: normal;
    font-weight: normal;
    line-height: 1;
}


.wrapper {
    text-align: left;
}

.page {
    padding-top: 150px;
    position: relative;
}

/* TOP LINKS */
.header-container.type3.header-newskin {
    border-top-width: 3px;
    border-top-style: solid;
    border-color: #131a22;
    margin-bottom: 50px;
	background-color: #ffffff;
}
.header-container.type3.header-newskin {
    position: fixed;
    width: 100%;
    z-index: 99;
    top: 0;
}
.top-links-container {
    background-color: #f0f0ed;
    padding: 3px 0;
    position: relative;
    z-index: 200;
}
.header-container.type3 .top-links-container {
	background-color: #fff;
	min-height: 33px;
}
.header-container.type3.header-newskin .top-links-container {
    border-bottom: #eeeeee solid 2px;
    padding: 3px 0;
}
.container {
    width: 100%;
    padding-right: 15px;
    padding-left: 15px;
    margin-right: auto;
    margin-left: auto;
}
@media (max-width: 1024px) {	
	.container {
		max-width: 100%;
	}
}

.header-container .form-language, 
.header-container .form-currency {
    display: block;
    margin-right: 8px;
}
.form-language.top-select {
    margin-top: 7px;
}
.form-language.top-select a {
    color: #000;
    font-weight: bold;
}

/* HEADER */
.header {
    position: relative;
    z-index: 101;
    text-align: left;
}
.header-container.type3.header-newskin .header {
    text-align: center;
}
@media (max-width: 767px) {
	.header {
		width: 100%;
	}
}
.header>.logo {
	display: inline-block;
}
.header-container.type3.header-newskin .header>.logo {
    margin: 15px 0;
}
.header .logo strong {
    position: absolute;
	top: -999em;
    left: -999em;
}
.header-container.type3.header-newskin .header .logo img {
    height: 50px;
	margin-top: -10px;
}

.header-container.type3.header-newskin .search-area {
    position: absolute;
}
@media (max-width: 991px) {
	.header-container.type3.header-newskin .search-area {
		left: 0;
		z-index: 2;
	}
}
@media (max-width: 1024px) {
	.header-container.type3.header-newskin .search-area {
		margin: 10px 10px;
		width: 94%;
		top: 40px;
	}
}
.search-icon {
    display: none !important;
}
.header-container.type3.header-newskin .header #search_mini_form {
    width: auto;
    margin: 0;
}
.header .form-search {
    border-radius: 20px;
	border: 1px solid #ccc;
}
.header .form-search {
    border-radius: 20px !important;
	background-color: #eee9e6;
	border-color: #ffffff;
}
@media (max-width: 991px) {
	.header-container.type3.header-newskin .header .form-search {
		position: absolute;
		top: 0;
		overflow: visible;
		border-width: 5px;
		width: 100%;
		left: 0;
		right: auto;
	}
}

/* HEADER WRAPPER */
@media (max-width: 991px) {
	.header-container .header-wrapper {
		display: none;
	}
}
.header .form-search #search {
    border: 0;
    height: 38px;
    background-color: transparent;
    padding: 10px 15px;
    color: #999;
    width: 100%;
    margin: 0;
    font-size: 13px;
    line-height: 20px;
    border-radius: 20px 0 0 20px;
}
.header-container.type3.header-newskin .header .form-search #search {
    height: 40px;
}

.mobile-nav.side-block {
    position: fixed;
    top: 0;
    left: -250px;
    width: 250px;
}
.header .form-search button.button {
    position: absolute;
	border: 0;
	background-color: transparent;
}
.header .form-search label,
.breadcrumbs {
    display: none;
}

critical-pdp.css

.product-image-carousel:not(.owl-loaded) {
	display: block!important;
}
.product-image-carousel:not(.owl-loaded) .item {
	display: none;
}
/* .owl-dots */
.product-image-carousel:not(.owl-loaded) .item {
	padding-bottom: 13px;
}

.product-image-carousel .item:after {
    content: '';
    display: block;
    width: 100%;
    height: 100%;
    position: absolute;
    z-index: 1;
    box-shadow: inset 20px 0 100px rgba(0,0,0,0.03);
    background-color: rgba(0,0,0,0.02);
    left: 0;
    top: 0;
}
.product-image-carousel:not(.owl-loaded) .item:first-child {
	display: block;
	padding-top: 100%;
	position: relative;
	width: 100%;
    background-color: rgba(0,0,0,0.02);
}
.product-image-carousel:not(.owl-loaded) .item img {
	position: absolute;
    display: block;
    width: 100%;
	top: 0;
}
#loading-mask {
    position: fixed;
}

.product-name {
    margin: 10px 0;
    font-size: 1em;
    font-weight: 400;
}
.product-view .product-shop > div {
    text-align: left;
}
@media (max-width: 1024px) {
	.product-view .product-name h1 {
		font-size: 18px;
		font-weight: 600;
		letter-spacing: -0.01em;
		color: #21293c;
		margin: 0 0 25px;
		line-height: 20px;
	}
}

.ratings {
    display: none;
}

table {
    background-color: transparent;
}
table {
    border: 0;
    border-spacing: 0;
    empty-cells: show;
    font-size: 100%;
}
caption, th, td {
    vertical-align: middle;
    text-align: left;
    font-weight: 400;
}
label {
    margin: 0;
    vertical-align: middle;
    color: #777;
    font-size: 13px;
    font-weight: 400;
}
label {
    color: #2d2d2d;
}

.data-table {
    width: 100%;
    border: 0;
}
.data-table.grouped-items-table {
    margin-bottom: 20px;
    border: 1px solid #dcdcdc;
}
.data-table tbody tr {
    border-left: 1px solid #dcdcdc;
    border-right: 1px solid #dcdcdc;
    background-color: #fff;
}
.product-type-grouped .data-table tbody th, 
.data-table tbody td {
    border-bottom: 0px solid #dcdcdc;
    border-right: 0px solid #dcdcdc;
    padding: 2px 10px;
    line-height: 1.3;
}
.data-table.grouped-items-table th, 
.data-table.grouped-items-table td {
    padding: 5px 0px;
}

.qty-holder {
    display: inline-block;
    vertical-align: middle;
    margin-right: 7px;
    width: 30px;
    position: relative;
    text-align: center;
}
.data-table .qty-holder, 
.data-table .add-to-cart-alt {
    position: relative;
    text-align: left;
    margin-right: 0;
}

input.input-text, select, textarea {
    background: #fff;
    border: 1px solid #ccc;
}
input.qty {
    margin-right: 1px;
    margin-left: 1px;
    display: inline-block;
    vertical-align: middle;
    height: 43px;
    font-size: 14px;
    text-align: center;
    color: #08c;
    border-color: #e1e1e1;
}
.data-table input.qty {
    color: #777;
    width: 50px;
    border-radius: 0;
    border-color: #ddd;
	font-size: 16px;
}

.price-box {
    min-height: 19px;
}
.product-view .price-box {
    margin: 0 !important;
}
.product-view .product-shop .price-box {
    float: right;
}
.product-view .product-shop .price-box .regular-price .price {
    font-size: 18px;
    font-weight: 700;
    font-family: sans-serif;
    color: #c30524;
}

.lead-time-message .notice {
    color: #74b436;
}
.notice {
    color: #e26703;
}

demo.php

<?php

function arrayToAttributeString( array $attr )
{
	$string = null;
	foreach ( $attr as $k => $v ) {
		$string	.= ' ' . $k . ( empty($v) ? null: '="' . $v . '"' );
	}
	
	return trim($string);
}

function doCriticalCss( $headHtml, array $criticalFiles=array() )
{
	if ( empty($criticalFiles) ) {
		return $headHtml;
	}
	
	$_noscript			= array();
	$_loop				= array(
		'link' => array('rel'=>'', 'type'=>'', 'href'=>'', 'media'=>''),
		'script' => array('src'=>'')
	);
	$_attributes		= array('rel'=>'', 'type'=>'', 'href'=>'', 'media'=>'', 'async'=>'', 'defer'=>'');
	$_allowedPreloads	= array('script','image','font','style');
	
	// determine stylesheets and scripts within our $headHtml string
	preg_match_all('|(<([a-z]+)[^>]+>)|', $headHtml, $matches);
	foreach( $matches[1] as $j => $elm )
	{
		$tag = $matches[2][$j];
		if ( !isset( $_loop[ $tag ] ) ) {
			continue;
		}
		
		$_attributes	= $attrs = $_loop[ $tag ];
		if ( !empty($_attributes) ) {
			preg_match_all('/(' . implode('|', array_keys( $_attributes ) ) . ')=("[^"]*")/i', $elm, $list, PREG_SET_ORDER);
			foreach ( $list as $opts ) {
				$attrs[ $opts[1] ]	= trim($opts[2],'"');
			}			
		}
		
		// only adjust/mutate links if non-printable stylesheet (so, no canonical)
		if ( $tag == 'link' && $attrs['rel'] == 'stylesheet' && $attrs['media'] !== 'print' ) {
		
			$media	= null;
			if ( strpos($attrs['media'],'(') !== false ) {
				$media	= $attrs['media'];
			}
			
			$attrs['media']		= 'print';
			$attrs['onload']	= 'this.media=\'' . ( $media ? $media: 'all' ) . '\';this.onload=null';
			
			// add the stylesheet to noscript, as we wan't to fall back to direct/render blocking styling when JS has been disabled by visitors
			$_noscript[]	= $elm;
			
			// and change original link-element to a lazyloading (onload) stylesheet-link
			$attrs			= array_filter( $attrs );
			$newStylesheet	= '<link ' . arrayToAttributeString( $attrs ) . ' />';
			$headHtml		= str_replace( $elm, $newStylesheet, $headHtml );
		}
		else if ( $tag == 'script' && !empty($attrs['src']) ) {
			// add defer to script
			$attrs['defer']	= '';
			$newScript		= '<script ' . arrayToAttributeString( $attrs ) . '>';
			$headHtml		= str_replace( $elm, $newScript, $headHtml );
		}
	}
	
	// echo critical css and noscript
	echo '
		<style type="text/css">' . str_replace( array("\n","\r","\t"), null, implode( null, array_map('file_get_contents', $criticalFiles ) ) ) . '</style>
		<noscript>' . implode( null, $_noscript) . '</noscript>';
	
	// return adjusted $headHtml
	return $headHtml;
}


$headHtml		= file_get_contents('getCssJsHtml.txt'); // Magento 1 function call: $this->getCssJsHtml();
$criticalCss	= array();
$criticalCss[]	= 'critical-all.css';
$criticalCss[]	= 'critical-pdp.css';

/*
// decide when to do critical magic in Magento 1
if ( Mage::registry('current_product') ) {
	// if on product page
	$criticalCss[]	= $skin_url.'critical-general.css';
	$criticalCss[]	= $skin_url.'critical-product.css';
}
else if ( Mage::registry('current_category') ) {
	// if on category page
	$criticalCss[]	= $skin_url.'critical-general.css';
	$criticalCss[]	= $skin_url.'critical-category.css';
}
else {
	// on other pages, such as text-only or homepage, do nothing special
}
*/

// inline critical css and adjust $headHtml accordingly
$headHtml = doCriticalCss( $headHtml, $criticalCss );

// business as usual:
echo $headHtml;

?>

getCssJsHtml.txt

<link rel="stylesheet" type="text/css" href="/media/css_secure/b96948b8dd0ef4b7b53a3e3e231a3824.css" />
<link rel="stylesheet" media="(min-width:500px;)" type="text/css" href="/media/css_secure/42b7842a9e58e6b85ee88eb738e39602.css" />
<link rel="canonical" href="..."/>
<!--[if gt IE 7]>
<link rel="stylesheet" type="text/css" href="/media/css_secure/49b5e70767b8445de9741aa24f9b76b7.css"media="all" />
<![endif]-->

<script src="/media/js_secure/main.js"></script>
<script defer src="/media/js_secure/defer.js"></script>

$skin_url = Mage::getBaseUrl(Mage_Core_Model_Store::URL_TYPE_SKIN);

Should work for all