DOC Document new startup theme

en/08_Changelogs/6.0.0.md

@@ -24,6 +24,7 @@ title: 6.0.0 (unreleased)
   - [Changes to `LeftAndMain` and its subclasses](#leftandmain-refactor)
   - [Changes to password validation](#password-validation)
   - [Status flags in the CMS](#status-flags-in-the-cms)
+  - [New default front-end theme](#theme)
   - [Other new features](#other-new-features)
 - [Dependency changes](#dependency-changes)
   - [`intervention/image` has been upgraded from v2 to v3](#intervention-image)
@@ -801,6 +802,16 @@ Status flags are displayed in breadcrumbs at the top of edit forms in the CMS, i
 
 See [status flags](/developer_guides/customising_the_admin_interface/status_flags/) for more information.
 
+### New default front-end theme {#theme}
+
+New projects created using `silverstripe/installer` will notice a new theme [`silverstripe/startup-theme`](https://packagist.org/packages/silverstripe/startup-theme) which replaces `silverstripe-themes/simple`.
+
+The new theme is visually very similar to the old one, but has been built from the ground up with cascading themes and customisability in mind. For example you can customise a lot of the styling by changing values of CSS variables.
+
+The new theme also outputs the `$ElementalArea` by default if you have [`dnadesign/silverstripe-elemental`](https://packagist.org/packages/dnadesign/silverstripe-elemental) installed, and exposes the [`$SilverStripeNavigator`](/developer_guides/templates/common_variables/#silverstripenavigator) for logged in users.
+
+Most projects will still benefit from a custom built theme, but this new theme should make it easier to test and validate PHP code changes in the early stages of a project and for module development.
+
 ### Other new features
 
 - Modules no longer need to have a root level `_config.php` or `_config` directory to be recognised as a Silverstripe CMS module. They will now be recognised as a module if they have a `composer.json` file with a `type` of `silverstripe-vendormodule` or `silverstripe-theme`.

en/12_Project_Governance/07_Supported_Modules.md

@@ -56,7 +56,7 @@ Supported PHP Module | Supported versions
 [colymba/gridfield-bulk-editing-tools](https://packagist.org/packages/colymba/gridfield-bulk-editing-tools) | 5
 [dnadesign/silverstripe-elemental](https://packagist.org/packages/dnadesign/silverstripe-elemental) | 6
 [dnadesign/silverstripe-elemental-userforms](https://packagist.org/packages/dnadesign/silverstripe-elemental-userforms) | 5
-[silverstripe-themes/simple](https://packagist.org/packages/silverstripe-themes/simple) | 3
+[silverstripe/startup-theme](https://packagist.org/packages/silverstripe/startup-theme) | 1
 [silverstripe/dynamodb](https://packagist.org/packages/silverstripe/dynamodb) | 6
 [silverstripe/gridfieldqueuedexport](https://packagist.org/packages/silverstripe/gridfieldqueuedexport) | 4
 [silverstripe/hybridsessions](https://packagist.org/packages/silverstripe/hybridsessions) | 4