diff --git a/src/app/MetaBrush/Action.hs b/src/app/MetaBrush/Action.hs
index 87d6b80..52b644b 100644
--- a/src/app/MetaBrush/Action.hs
+++ b/src/app/MetaBrush/Action.hs
@@ -1,5 +1,7 @@
 {-# LANGUAGE OverloadedStrings #-}
 
+{-# LANGUAGE ScopedTypeVariables #-}
+
 module MetaBrush.Action where
 
 -- base
@@ -9,8 +11,6 @@ import Control.Monad.ST
   ( RealWorld )
 import Data.Foldable
   ( for_ )
-import Data.Int
-  ( Int32 )
 import Data.List
   ( uncons )
 import Data.Maybe
@@ -231,32 +231,47 @@ instance HandleAction OpenFile where
             for_ fileNames $ \ filePath -> do
               mbDoc <- loadDocument uniqueSupply filePath
               case mbDoc of
-                Left errMessage -> warningDialog window filePath errMessage
+                Left errMessage -> openFileWarningDialog window filePath errMessage
                 Right doc -> do
                   let newDocHist = newHistory doc
                   newFileTab uiElts vars (Just newDocHist) tabLoc
                   updateHistoryState uiElts (Just newDocHist)
           Nothing -> return ()
 
-warningDialog
-  :: ( Show errMess, GTK.IsWindow window )
-  => window -> FilePath -> errMess -> IO ()
-warningDialog window filePath errMess = do
-  -- GTK 4 TODO: use Window
-  dialog <- GTK.new GTK.MessageDialog []
-  GTK.setMessageDialogText dialog
-    ( "Could not load file at " <> Text.pack filePath <> ":\n" <> Text.pack ( show errMess ) )
-  GTK.setMessageDialogMessageType dialog GTK.MessageTypeWarning
-  GTK.setWindowResizable dialog True
-  GTK.setWindowDecorated dialog False
-  GTK.windowSetTransientFor dialog ( Just window )
-  GTK.windowSetModal dialog True
-  widgetAddClasses dialog [ "metabrush", "bg", "plain", "text", "dialog" ]
-  closeButton <- GTK.dialogAddButton dialog "OK" 1
+openFileWarningDialog
+  :: GTK.IsWindow window
+  => window -> FilePath -> String -> IO ()
+openFileWarningDialog window filePath errMess = do
+
+  dialogWindow <- GTK.windowNew
+  GTK.setWindowDecorated dialogWindow False
+  GTK.windowSetTransientFor dialogWindow (Just window)
+
+  contentBox <- GTK.boxNew GTK.OrientationVertical 30
+  GTK.widgetSetMarginStart  contentBox 20
+  GTK.widgetSetMarginEnd    contentBox 20
+  GTK.widgetSetMarginTop    contentBox 20
+  GTK.widgetSetMarginBottom contentBox 20
+
+  label <- GTK.labelNew $ Just $ "Could not load file at " <> Text.pack filePath <> ":\n" <> Text.pack errMess
+  GTK.boxAppend contentBox label
+
+  closeButton <- GTK.buttonNew
+  GTK.buttonSetLabel closeButton "OK"
+  GTK.boxAppend contentBox closeButton
+
+  GTK.windowSetChild dialogWindow (Just contentBox)
+
+  widgetAddClasses dialogWindow ["metabrush", "bg", "plain", "text", "dialog"]
   widgetAddClass closeButton "dialogButton"
-  widgetShow dialog
-  void $ GTK.afterDialogResponse dialog \ _ -> do
-    GTK.windowDestroy dialog
+
+  void $ GTK.onButtonClicked closeButton $ do
+    GTK.windowDestroy dialogWindow
+
+  GTK.widgetSetVisible dialogWindow True
+
+  -- TODO: make the dialog draggable.
+  -- See https://discourse.gnome.org/t/enabling-window-dragging-on-specific-elements-in-gtk-4/5731/4
 
 -----------------
 -- Open folder --
@@ -286,7 +301,7 @@ instance HandleAction OpenFolder where
               for_ filePaths \ filePath -> when ( takeExtension filePath == ".mb" ) do
                 mbDoc <- loadDocument uniqueSupply ( folderPath </> filePath )
                 case mbDoc of
-                  Left errMessage -> warningDialog window filePath errMessage
+                  Left errMessage -> openFileWarningDialog window filePath errMessage
                   Right doc -> do
                     let
                       newDocHist :: DocumentHistory
@@ -414,11 +429,6 @@ data Close
     { docToClose :: !Unique }
   deriving stock Show
 
-pattern JustClose, SaveAndClose, CancelClose :: Int32
-pattern JustClose    = 1
-pattern SaveAndClose = 2
-pattern CancelClose  = 3
-
 instance HandleAction Close where
   handleAction
     uiElts@( UIElements {..} )
@@ -436,28 +446,49 @@ instance HandleAction Close where
         Just ( Document { displayName, documentUnique, documentContent }, isActiveDoc )
           | unsavedChanges documentContent
           -> do
-            -- GTK 4 TODO: use Window
-            dialog <- GTK.new GTK.MessageDialog []
-            GTK.setMessageDialogText dialog ( " \n\"" <> displayName <> "\" contains unsaved changes.\nClose anyway?" )
-            GTK.setMessageDialogMessageType dialog GTK.MessageTypeQuestion
-            GTK.setWindowResizable dialog False
-            GTK.setWindowDecorated dialog False
-            GTK.windowSetTransientFor dialog ( Just window )
-            GTK.windowSetModal dialog True
-            widgetAddClasses dialog [ "metabrush", "bg", "plain", "text", "dialog" ]
-            closeButton  <- GTK.dialogAddButton dialog "Close"          JustClose
-            saveButton   <- GTK.dialogAddButton dialog "Save and close" SaveAndClose
-            cancelButton <- GTK.dialogAddButton dialog "Cancel"         CancelClose
-            GTK.dialogSetDefaultResponse dialog JustClose
-            for_ [ closeButton, saveButton, cancelButton ]
-              ( `widgetAddClass` "dialogButton" )
-            widgetShow dialog
-            void $ GTK.onDialogResponse dialog \ choice -> do
-              case choice of
-                JustClose    -> closeDocument isActiveDoc documentUnique
-                SaveAndClose -> save uiElts vars False
-                _            -> pure ()
-              GTK.windowDestroy dialog
+            dialogWindow <- GTK.windowNew
+            GTK.setWindowDecorated dialogWindow False
+            GTK.windowSetTransientFor dialogWindow (Just window)
+
+            contentBox <- GTK.boxNew GTK.OrientationVertical 30
+            GTK.widgetSetMarginStart  contentBox 20
+            GTK.widgetSetMarginEnd    contentBox 20
+            GTK.widgetSetMarginTop    contentBox 20
+            GTK.widgetSetMarginBottom contentBox 20
+            GTK.windowSetChild dialogWindow (Just contentBox)
+
+            label <- GTK.labelNew $ Just $ "\n\"" <> displayName <> "\" contains unsaved changes.\nClose anyway?"
+            GTK.boxAppend contentBox label
+
+            buttonBox <- GTK.boxNew GTK.OrientationHorizontal 0
+
+            GTK.boxAppend contentBox buttonBox
+
+            closeButton <- GTK.buttonNew
+            GTK.buttonSetLabel closeButton "Close"
+            GTK.boxAppend buttonBox closeButton
+            saveCloseButton <- GTK.buttonNew
+            GTK.buttonSetLabel saveCloseButton "Save and close"
+            GTK.boxAppend buttonBox saveCloseButton
+            cancelButton <- GTK.buttonNew
+            GTK.buttonSetLabel cancelButton "Cancel"
+            GTK.boxAppend buttonBox cancelButton
+
+            widgetAddClasses dialogWindow ["metabrush", "bg", "plain", "text", "dialog"]
+            for_ [closeButton, saveCloseButton, cancelButton] \ button ->
+              widgetAddClass button "dialogButton"
+
+            void $ GTK.onButtonClicked closeButton $ do
+              closeDocument isActiveDoc documentUnique
+              GTK.windowDestroy dialogWindow
+            void $ GTK.onButtonClicked saveCloseButton $ do
+              save uiElts vars False
+              GTK.windowDestroy dialogWindow
+            void $ GTK.onButtonClicked cancelButton $ do
+              GTK.windowDestroy dialogWindow
+
+            GTK.widgetSetVisible dialogWindow True
+
           | otherwise
           -> closeDocument isActiveDoc documentUnique