brand shortcode light/dark updates

(cherry picked from commit 1c279a0)

Author: gordonwoodhull

docs/authoring/brand.qmd

@@ -586,10 +586,13 @@ Beyond the automatic application of your brand file, you can also directly acces
 
 Some values from the `_brand.yml` configuration file can be accessed via the `brand` shortcode. In particular, you can access colors and logos by name:
 
--   Use `{{{< brand color COLOR_NAME BRAND_MODE >}}}` to return the brand color named `COLOR_NAME` as a string.
--   Use `{{{< brand logo LOGO_NAME BRAND_MODE >}}}` to return the brand logo named `LOGO_NAME` as an image.
+-   Use `{{{< brand color COLOR_NAME VARIANT >}}}` to return the brand color named `COLOR_NAME` as a string.
+-   Use `{{{< brand logo LOGO_NAME VARIANT >}}}` to return the brand logo named `LOGO_NAME` as an image.
 
-The `BRAND_MODE` is optional and defaults to `light`. To return the color from the [dark brand](#dark-brand) use `dark`.
+`VARIANT` is optional:
+
+- For the `brand color` shortcode, the default is `light`. To return the color from the [dark brand](#dark-brand) use `dark`.
+- For the `brand logo` shortcode, the default is `both`, which will add both light and dark logos with appropriate classes
 
 For example, you could use the shortcode to place a brand image you've named `icon` in a dashboard sidebar: