def scroll_one_line_down(event):
    """
    scroll_offset += 1
    """
    w = event.app.layout.current_window
    b = event.app.current_buffer
    if w:
        if w.render_info:
            info = w.render_info
            if w.vertical_scroll < info.content_height - info.window_height:
                if (info.cursor_position.y <= info.
                    configured_scroll_offsets.top):
                    b.cursor_position += b.document.get_cursor_down_position()
                w.vertical_scroll += 1
