Issue #3525108 by bmango, grimreaper: Document limitations.

README.md

@@ -11,6 +11,7 @@ See the [docs](./docs) folder for more detailed documentation on:
 - [form API](./docs/Forms.md)
 - [modal](./docs/Modal.md)
 - [what is out of scope](./docs/Out-of-scope.md)
+- [limitations](./docs/Limitations.md)
 
 
 ## Requirements

docs/Limitations.md

+# Limitations
+
+Some site building features do not work in specific cases.
+
+
+## UI Styles Block
+
+The **Site branding** block can't receive styles as its content is handled
+in a specific manner in [Core](https://git.drupalcode.org/project/drupal/-/blob/11.x/core/modules/system/templates/block--system-branding-block.html.twig?ref_type=heads).
+And so it does not use the `attributes` and `title_attributes` variables.
+
+
+## UI Styles Page
+
+The **Navigation (Collapsible)** region can't receive styles as its wrapper had
+been removed to allow proper flex effects on the blocks inside this region.