Invalid HTML detected in WP core by w3.org validator

[wordmax]

Using latest version of WordPress & Blocksy theme with very few modifications or plugins. I notified Blocksy of an invalid HTML detected by validator.w3.org and the theme developers say that the WordPress core is actually the cause, not the theme.

Here is the code that produces invalid HTML at w3.org:

<style>.wp-container-1 .alignleft { float: left; margin-right: 2em; }.wp-container-1 .alignright { float: right; margin-left: 2em; }</style>
<style>.wp-container-2 .alignleft { float: left; margin-right: 2em; }.wp-container-2 .alignright { float: right; margin-left: 2em; }</style>
<style>.wp-container-3 .alignleft { float: left; margin-right: 2em; }.wp-container-3 .alignright { float: right; margin-left: 2em; }</style>

[wordmax]

screenshot of html validation errors at w3

[audrasjb]

Hello and thank you for opening this ticket.
This was already reported in #55375 and it was reported on Gutenberg GitHub repository.

Closing this as duplicate. Thanks again!