add highlighting-css-dark option

MANUAL.txt

@@ -837,6 +837,12 @@ header when requesting a document from a URL:
     To generate the JSON version of an existing style,
     use `--print-highlight-style`.
 
+`--highlight-style-dark=`*STYLE*|*FILE*
+
+:   Specifies the coloring style to be used in highlighted source code
+    in [dark mode] for HTML-based output formats. The default is `breezeDark`.
+    See `--highlight-style` for more information.
+
 `--print-highlight-style=`*STYLE*|*FILE*
 
 :   Prints a JSON version of a highlighting style, which can
@@ -6202,6 +6208,10 @@ scheme used by the Python library pygments (though pygments is not actually
 used to do the highlighting).  To see a list of highlight styles,
 type `pandoc --list-highlight-styles`.
 
+For HTML-based output formats, the color scheme used for [dark mode]
+can be selected using the `--highlight-style-dark` option.
+It defaults to `breezeDark`.
+
 If you are not satisfied with the predefined styles, you can
 use `--print-highlight-style` to generate a JSON `.theme` file which
 can be modified and used as the argument to `--highlight-style`. To
@@ -6223,6 +6233,7 @@ definitions](https://github.com/KDE/syntax-highlighting/tree/master/data/syntax)
 To disable highlighting, use the `--no-highlight` option.
 
 [skylighting]: https://github.com/jgm/skylighting
+[dark mode]: https://developer.mozilla.org/en-US/docs/Web/CSS/@media/prefers-color-scheme
 
 # Custom Styles
 

src/Text/Pandoc/App/CommandLineOptions.hs

@@ -319,7 +319,9 @@ options =
 
     , Option "" ["no-highlight"]
                 (NoArg
-                 (\opt -> return opt { optHighlightStyle = Nothing }))
+                 (\opt -> return opt { optHighlightStyle     = Nothing
+                                     , optHighlightStyleDark = Nothing
+                                     }))
                  "" -- "Don't highlight source code"
 
     , Option "" ["highlight-style"]
@@ -330,6 +332,14 @@ options =
                  "STYLE|FILE")
                  "" -- "Style for highlighted code"
 
+    , Option "" ["highlight-style-dark"]
+                (ReqArg
+                 (\arg opt ->
+                     return opt{ optHighlightStyleDark = Just $
+                                 T.pack $ normalizePath arg })
+                 "STYLE|FILE")
+                 "" -- "Style for highlighted code in dark mode"
+
     , Option "" ["syntax-definition"]
                 (ReqArg
                  (\arg opt -> do

src/Text/Pandoc/App/Opt.hs

@@ -107,6 +107,7 @@ data Opt = Opt
     , optSelfContained         :: Bool    -- ^ Make HTML accessible offline
     , optHtmlQTags             :: Bool    -- ^ Use <q> tags in HTML
     , optHighlightStyle        :: Maybe Text -- ^ Style to use for highlighted code
+    , optHighlightStyleDark    :: Maybe Text -- ^ Style to use for highlighted code in dark mode
     , optSyntaxDefinitions     :: [FilePath]  -- ^ xml syntax defs to load
     , optTopLevelDivision      :: TopLevelDivision -- ^ Type of the top-level divisions
     , optHTMLMathMethod        :: HTMLMathMethod -- ^ Method to print HTML math
@@ -417,6 +418,8 @@ doOpt (k',v) = do
       parseYAML v >>= \x -> return (\o -> o{ optHtmlQTags = x })
     "highlight-style" ->
       parseYAML v >>= \x -> return (\o -> o{ optHighlightStyle = x })
+    "highlight-style-dark" ->
+      parseYAML v >>= \x -> return (\o -> o{ optHighlightStyleDark = x })
     "syntax-definition" ->
       (parseYAML v >>= \x ->
                 return (\o -> o{ optSyntaxDefinitions =
@@ -620,6 +623,7 @@ defaultOpts = Opt
     , optSelfContained         = False
     , optHtmlQTags             = False
     , optHighlightStyle        = Just "pygments"
+    , optHighlightStyleDark    = Just "breezeDark"
     , optSyntaxDefinitions     = []
     , optTopLevelDivision      = TopLevelDefault
     , optHTMLMathMethod        = PlainMath

src/Text/Pandoc/App/OutputSettings.hs

@@ -109,6 +109,7 @@ optToOutputSettings opts = do
                      (optSyntaxDefinitions opts)
 
   hlStyle <- traverse (lookupHighlightStyle . T.unpack) $ optHighlightStyle opts
+  hlStyleDark <- traverse (lookupHighlightStyle . T.unpack) $ optHighlightStyleDark opts
 
   let setVariableM k v = return . setVariable k v
 
@@ -202,6 +203,7 @@ optToOutputSettings opts = do
         , writerListings         = optListings opts
         , writerSlideLevel       = optSlideLevel opts
         , writerHighlightStyle   = hlStyle
+        , writerHighlightStyleDark = hlStyleDark
         , writerSetextHeaders    = optSetextHeaders opts
         , writerEpubSubdirectory = T.pack $ optEpubSubdirectory opts
         , writerEpubMetadata     = epubMetadata

src/Text/Pandoc/Options.hs

@@ -45,7 +45,7 @@ import GHC.Generics (Generic)
 import Skylighting (SyntaxMap, defaultSyntaxMap)
 import Text.DocTemplates (Context(..), Template)
 import Text.Pandoc.Extensions
-import Text.Pandoc.Highlighting (Style, pygments)
+import Text.Pandoc.Highlighting (Style, breezeDark, pygments)
 import Text.Pandoc.Shared (camelCaseStrToHyphenated)
 import Data.Aeson.TH (deriveJSON, defaultOptions, Options(..),
                       SumEncoding(..))
@@ -255,6 +255,7 @@ data WriterOptions = WriterOptions
   , writerListings          :: Bool       -- ^ Use listings package for code
   , writerHighlightStyle    :: Maybe Style  -- ^ Style to use for highlighting
                                            -- (Nothing = no highlighting)
+  , writerHighlightStyleDark :: Maybe Style  -- ^ Style to use for highlighting dark mode
   , writerSetextHeaders     :: Bool       -- ^ Use setext headers for levels 1-2 in markdown
   , writerEpubSubdirectory  :: Text       -- ^ Subdir for epub in OCF
   , writerEpubMetadata      :: Maybe Text -- ^ Metadata to include in EPUB
@@ -290,6 +291,7 @@ instance Default WriterOptions where
                       , writerTopLevelDivision = TopLevelDefault
                       , writerListings         = False
                       , writerHighlightStyle   = Just pygments
+                      , writerHighlightStyleDark = Just breezeDark
                       , writerSetextHeaders    = False
                       , writerEpubSubdirectory = "EPUB"
                       , writerEpubMetadata     = Nothing

src/Text/Pandoc/Writers/HTML.hs

@@ -324,8 +324,10 @@ pandocToHtml opts (Pandoc meta blocks) = do
                                 Nothing  -> id
                       else id) .
                   (if stHighlighting st
-                      then defField "highlighting-css-dark"
-                             (T.pack $ styleToCss breezeDark)
+                      then case writerHighlightStyleDark opts of
+                                Just sty -> defField "highlighting-css-dark"
+                                              (T.pack $ styleToCss sty)
+                                Nothing  -> id
                       else id) .
                   (if stCsl st
                       then defField "csl-css" True .