Feature: #92616 - Bootstrap v5¶
TYPO3s Backend is powered with Bootstrap v5 (https://getbootstrap.com).
Previous versions ran with Bootstrap v3. A lots of changes and improvements are included, especially regarding simplification of building Layouts and Containers.
It is important during updates of custom backend modules to study the Bootstrap Migration guidelines and adapt accordingly:
TYPO3 Core still includes some legacy styling and functionality to provide compatibility, but backend markup and code will be adapted during further TYPO3 v11 development to simplify the HTML and CSS code shipped with TYPO3 Core.