Modernizing default Drupal Core markup and CSS

During the Drupal 8 development cycle, the community rallied to create modernized default markup in Classy. This was a great improvement on Drupals frontend developer experience compared to previous releases. As a result of these changes, we were able to get many frontend developers move from using contributed base themes to using Classy. However, since Drupal 8 shipped, we haven't been able to make improvements to Classy in order to keep themes built on top of it working without any setbacks. Given that Drupal 8 was released almost 6 years ago, it is a good time to start looking into how we could modernize the default markup. On this session I will explain what the plan is for allowing changes to be made to our default markup without causing issues on existing themes and how to get started contributing to a better default markup.