diff --git a/app/Commands/Html.hs b/app/Commands/Html.hs
index 3590e99566..bc0d56900c 100644
--- a/app/Commands/Html.hs
+++ b/app/Commands/Html.hs
@@ -28,6 +28,7 @@ parseHtml = do
           <> value Ayu
           <> showDefault
           <> help "selects a theme: ayu (light); nord (dark)"
+          <> completeWith (map show allThemes)
       )
   _htmlOutputDir <-
     option
@@ -46,8 +47,10 @@ parseHtml = do
       )
   pure HtmlOptions {..}
   where
+    allThemes :: [Theme]
+    allThemes = allElements
     parseTheme :: String -> Either String Theme
-    parseTheme s = case s of
+    parseTheme s = case map toLower s of
       "nord" -> Right Nord
       "ayu" -> Right Ayu
       _ -> Left $ "unrecognised theme: " <> s
diff --git a/src/Juvix/Compiler/Backend/Html/Data/Theme.hs b/src/Juvix/Compiler/Backend/Html/Data/Theme.hs
index 7ca5415cab..4b899e61a8 100644
--- a/src/Juvix/Compiler/Backend/Html/Data/Theme.hs
+++ b/src/Juvix/Compiler/Backend/Html/Data/Theme.hs
@@ -5,7 +5,7 @@ import Juvix.Prelude
 data Theme
   = Nord
   | Ayu
-  deriving stock (Show)
+  deriving stock (Show, Enum, Bounded)
 
 data HtmlKind
   = HtmlDoc