Magento 2.3.3 - using CSS Critical Path throws strange syntax in source code - how can we solve this?

Question

Google Page Speed told us, that we have rendering blocking CSS.

Now we try to solve this with CSS Critical Path activated.

We have created a Critical.css file

We have integated the same in our Theme.

All works fine, we try which styles are important and which CSS can load later.

BUT now the source code coming from CSS Critical Path in general adds a weird dot, (like a ".") to the code between media="all" and onload...:

link rel="preload" as="style" media="all" . onload="this.onload=null;this.rel='stylesheet'"href="http:

See here as well.

enter image description here

When running validator.w3.org it says

Error: Attribute . not allowed on element link at this point.

and also

Warning: Attribute . is not serializable as XML 1.0.

So this funny dot (.) is there.

Does anyone of you experts have a clue why this is there and how we could get rid of it?

Any help is so appreciated.

Warm regards

• Ben Crook: How have you added this CSS file?
• Ben: Hi Ben, we have added the same as per "The ‘critical’ CSS file should be located in app/design/frontend/<your_vendor_name>/<your_theme_name>/web/css/critical.css " like mentioned here: devdocs.magento.com/guides/v2.3/frontend-dev-guide/css-topics/… - using this Penthouse generator jonassebastianohlsson.com/criticalpathcssgenerator Best regards
• Ben Crook: Ah I completely forgot M2 supports critical CSS out the box. I haven't seen this problem before but I will be setting critical CSS up on a project soon so if I run into the problem and find a solution I'll provide the answer here.
• Eubie Aluad: Hi guys did you already resolved the issue?

Answer 1

It is a bug in Magento, fixed in the new version 2.4 see here https://github.com/magento/magento2/pull/26764/commits/f9697f509ae09f5c9e0f0d7b1a2de7ed9a53fc16