src/Tools/jEdit/src/graphview_dockable.scala

         val visualizer = new isabelle.graphview.Visualizer(model) {
           override def foreground_color = view.getTextArea.getPainter.getForeground
           override def background_color = view.getTextArea.getPainter.getBackground
           override def selection_color = view.getTextArea.getPainter.getSelectionColor
           override def error_color = PIDE.options.color_value("error_color")
+          override def font_size = view.getTextArea.getPainter.getFont.getSize
+          override def font = view.getTextArea.getPainter.getFont
         }
         new isabelle.graphview.Main_Panel(model, visualizer) {
           override def make_tooltip(parent: JComponent, x: Int, y: Int, body: XML.Body): String =
           {
             Pretty_Tooltip.invoke(() =>