Inline Critical CSS: Cut Your FCP in Half

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Inline Critical CSS: Cut Your First Contentful Paint in Half

January 2026 13 min read

I’m Jacob Campbell, and if I could only make one speed fix on a slow site, it would be inlining critical CSS. External stylesheets are render-blocking: the browser refuses to paint anything until they download. Inline the little bit of CSS the first screen needs, and the page can start painting almost immediately. Here’s how it works and why it’s the biggest First Contentful Paint win available.

<style>
  /* critical.css contents here */
  body { font-family: 'Inter', sans-serif; background: #0a0a0a; }
  .hero { min-height: 100vh; display: flex; align-items: center; }
  .btn { background: #3b82f6; padding: 12px 28px; border-radius: 40px; }
</style>

<link rel="preload" href="full-styles.css" as="style" onload="this.onload=null;this.rel='stylesheet'">
<noscript><link rel="stylesheet" href="full-styles.css"></noscript>

<?php
// generate_critical_css.php – run after CSS changes
require 'vendor/autoload.php';

use Symfony\Component\DomCrawler\Crawler;

$html = file_get_contents('https://yourdomain.com/');
$crawler = new Crawler($html);

// Find all style and link tags
$critical = '';
$crawler->filter('style, link[rel="stylesheet"]')->each(function ($node) use (&$critical) {
    if ($node->nodeName() === 'style') {
        $critical .= $node->text();
    } else {
        $href = $node->attr('href');
        $css = file_get_contents($href);
        $critical .= $css;
    }
});

// Simple heuristic: only keep rules used on the first 1000px height
// (For a real solution, use a library like `peterjmit/critical-css`)
file_put_contents('critical.css', $critical);
?>

composer require stripe/stripe-php

<?php
require 'vendor/autoload.php';
\Stripe\Stripe::setApiKey('sk_live_your_secret_key');

$checkout = \Stripe\Checkout\Session::create([
    'payment_method_types' => ['card'],
    'line_items' => [[
        'price_data' => [
            'currency' => 'usd',
            'product_data' => ['name' => 'Custom PHP Website – Business Pro'],
            'unit_amount' => 175000, // $1,750
        ],
        'quantity' => 1,
    ]],
    'mode' => 'payment',
    'success_url' => 'https://built2winweb.com/success?session_id={CHECKOUT_SESSION_ID}',
    'cancel_url' => 'https://built2winweb.com/cancel',
    'metadata' => ['package' => 'business']
]);
header("Location: " . $checkout->url);
exit;
?>

<?php
$payload = file_get_contents('php://input');
$sig_header = $_SERVER['HTTP_STRIPE_SIGNATURE'];
$webhook_secret = 'whsec_your_webhook_secret';

try {
    $event = \Stripe\Webhook::constructEvent($payload, $sig_header, $webhook_secret);
} catch (\UnexpectedValueException $e) {
    http_response_code(400);
    exit();
}

if ($event->type === 'checkout.session.completed') {
    $session = $event->data->object;
    // Send email to client, create account, etc.
    mail('client@example.com', 'Payment Received', 'Package: ' . $session->metadata->package);
}
http_response_code(200);
?>