update glossary (#16418)

dark mode
connection validation

docs/glossary/README.md

@@ -102,6 +102,10 @@ OpenProject can be installed either [on-premises](#on-premises) (available for b
 
 Community edition is defined as the main and free-of-charge edition of OpenProject software. It is installed [on-premises](#on-premises) and therefore self-managed. Benefit from a wide range of features and data sovereignty in a free and open source project management software. The Community edition is actively maintained and is continuously being further developed. [Read more about OpenProject Community edition](https://www.openproject.org/community-edition/).
 
+### Connection validation
+
+The connection validation in OpenProject is available for the storage integrations with [Nextcloud](#nextcloud-integration) and [OneDrive/SharePoint](#onedrivesharepoint-integration). It is a manually triggered test to check the connection between OpenProject and the respective storage. [Read more about health status checks for OpenProject's external file storages](../system-admin-guide/files/external-file-storages/health-status/).
+
 ### Custom action
 
 A custom action in OpenProject is defined as customizable buttons which trigger a certain action upon work packages. Custom actions are included in the [Enterprise](#enterprise-add-on) edition of OpenProject and part of automated *workflows*. Custom actions support you to easily update several work package attributes at once – with a single click.
@@ -129,6 +133,10 @@ A custom query in OpenProject consists of saved [filters](#filters), sort criter
 
 ## D
 
+### Dark mode
+
+The dark mode for OpenProject is a personal setting to display the application in a dark theme. Other available modes are the regular light mode and the (light) [high contrast mode](#high-contrast-mode). [Read in our documentation how to enable dark mode](../getting-started/my-account/#select-the-dark-mode).
+
 ### Dashboard
 
 A dashboard is defined as an overview page in a software. In OpenProject, you have several options to create dashboards: