diff --git a/docs/admin_docs/configuration/theming.mdx b/docs/admin_docs/configuration/theming.mdx
index 46e30e58b16..faee522163a 100644
--- a/docs/admin_docs/configuration/theming.mdx
+++ b/docs/admin_docs/configuration/theming.mdx
@@ -88,6 +88,27 @@ THEME_DARK = {
 # - OS preference detection is automatically enabled
 ```
 
+### Default Theme Mode
+
+By default, Superset mimics the visitor's OS/browser preference (light or dark) for
+sessions that don't have a saved user preference. Use `THEME_DEFAULT_MODE` to override
+that starting point instance-wide for the standard application:
+
+```python
+# Default theme mode for sessions without a saved user preference.
+# One of "default" (always light), "dark" (always dark), or "system" (mimic OS preference).
+THEME_DEFAULT_MODE = "dark"
+```
+
+- `"system"` (the default) preserves the existing behavior of following the OS/browser
+  preference, provided a dark theme is configured (`THEME_DARK` is not `None`). If no dark
+  theme is available, Superset always starts in light mode regardless of this setting.
+- `"default"` or `"dark"` forces that starting mode for first-time visitors; users can still switch themes manually afterward if both `THEME_DEFAULT` and `THEME_DARK` are available.
+- A user's own saved preference, once they toggle the theme switcher, always takes precedence over `THEME_DEFAULT_MODE`.
+- `THEME_DEFAULT_MODE` has no effect on embedded dashboards: the embed SDK sets the
+  starting mode via its own `themeMode` URL parameter, which takes precedence and falls
+  back to light mode when the parameter is absent.
+
 ### App Branding
 
 The application name shown in the browser title bar and navigation can be