preferred-dark-theme defaults to default-theme

book-example/src/format/config.md

@@ -150,8 +150,10 @@ The following configuration options are available:
   files with the ones found in the specified folder.
 - **default-theme:** The theme color scheme to select by default in the
   'Change Theme' dropdown. Defaults to `light`.
-- **preferred-dark-theme:** The default theme to use if the browser
+- **preferred-dark-theme:** The default dark theme. This theme will be used if
-  requests the dark version of the site. Defaults to `navy`.
+  the browser requests the dark version of the site via the
+  ['prefers-color-scheme'](https://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-color-scheme)
+  CSS media query. Defaults to the same theme as `default-theme`.
 - **curly-quotes:** Convert straight quotes to curly quotes, except for those
   that occur in code blocks and code spans. Defaults to `false`.
 - **mathjax-support:** Adds support for [MathJax](mathjax.md). Defaults to

src/config.rs

@@ -420,10 +420,8 @@ pub struct HtmlConfig {
     pub theme: Option<PathBuf>,
     /// The default theme to use, defaults to 'light'
     pub default_theme: Option<String>,
-    /// The default dark theme.
+    /// The theme to use if the browser requests the dark version of the site.
-    /// This theme will be used if the browser requests a dark theme
+    /// Defaults to the same as 'default_theme'
-    /// via the 'prefers-color-scheme' CSS media query.
-    /// Defaults to 'navy'.
     pub preferred_dark_theme: Option<String>,
     /// Use "smart quotes" instead of the usual `"` character.
     pub curly_quotes: bool,

src/renderer/html_handlebars/hbs_renderer.rs

@@ -409,7 +409,7 @@ fn make_data(
 
     let preferred_dark_theme = match html_config.preferred_dark_theme {
         Some(ref theme) => theme,
-        None => "navy",
+        None => default_theme,
     };
     data.insert(
         "preferred_dark_theme".to_owned(),