diff --git a/docs/SUMMARY.md b/docs/SUMMARY.md
index 4e2edea..4bd84cb 100644
--- a/docs/SUMMARY.md
+++ b/docs/SUMMARY.md
@@ -10,6 +10,7 @@
     - [Query Syntax](user/investigate/query-syntax.md)
   - [Manage](user/manage.md)
   - [Operate](user/operate.md)
+  - [Appearance](user/appearance.md)
 
 ---
 
diff --git a/docs/user/README.md b/docs/user/README.md
index 18f95e1..b79ff01 100644
--- a/docs/user/README.md
+++ b/docs/user/README.md
@@ -23,3 +23,5 @@ Osprey's tools are categorized into three primary functions:
 - [Bulk Job History](operate.md#bulk-job-history): review past bulk jobs and their results
 
 The sidebar can be collapsed to a narrow icon-only strip using the toggle at the bottom. Its state persists between sessions.
+
+The interface supports light and dark themes, see [Appearance](appearance.md) for details.
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diff --git a/docs/user/appearance.md b/docs/user/appearance.md
new file mode 100644
index 0000000..710f976
--- /dev/null
+++ b/docs/user/appearance.md
@@ -0,0 +1,19 @@
+# Appearance
+
+Osprey supports light and dark themes. By default, the interface follows your OS or browser colour-scheme preference. You can override this at any time using the theme toggle in the navigation bar.
+
+## Changing the theme
+
+The theme toggle is in the top-right area of the navigation bar. It offers three options:
+
+| Option | Icon | Behaviour |
+|--------|------|-----------|
+| **Light** | ☀ Sun | Always use the light theme |
+| **System** | 🖥 Desktop | Follow the OS/browser preference *(default)* |
+| **Dark** | ☾ Moon | Always use the dark theme |
+
+Your choice is saved in the browser and persists across sessions. Clearing browser storage resets it to **System**.
+
+## System preference
+
+When set to **System**, Osprey listens for OS colour-scheme changes in real time. Switching your OS between light and dark mode while Osprey is open takes effect immediately, no page reload required.
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