Modify the code so that the "S", "I", "E", "D" butonns to be flat. Python Code: class Header:
    """Class for handling header UI."""

    DATA_TYPE_OPTIONS = ["string", "integer", "float", "boolean"]

    def __init__(self, root: tk.Tk, app: 'TableApp'):
        self.root = root
        self.app = app
        self.style = app.style
        self.colors = app.colors
        self.fonts = app.fonts
        self.dimensions = app.dimensions
        self.table_name_label = None
        self.lower_header_frame = None
        self.result = None
        self._setup_header()

    def _setup_header(self) -> None:
        header_frame = self._setup_main_frame()
        self._setup_upper_section(header_frame)
        self._setup_lower_section(header_frame)

    def _setup_main_frame(self) -> tk.Frame:
        header_frame = create_frame(parent=self.root, width=None, bg=self.colors["background"])
        header_frame.grid(row=0, column=1, columnspan=2, sticky="ew")
        header_frame.config(height=self.dimensions["header_height"])
        header_frame.grid_propagate(False)
        header_frame.grid_rowconfigure(0, weight=0)
        header_frame.grid_rowconfigure(1, weight=0)
        for i in range(5):
            header_frame.grid_columnconfigure(i, weight=1 if i == 4 else 0)
        return header_frame

    def _setup_upper_section(self, parent: tk.Frame) -> None:
        upper_frame = create_frame(parent=parent, width=None, bg=self.colors["background"])
        upper_frame.grid(row=0, column=0, columnspan=6, sticky="ew", pady=(0, 10))
        upper_frame.grid_columnconfigure(5, weight=1)
        self._add_upper_content(upper_frame)

    def _add_upper_content(self, frame: tk.Frame) -> None:
        tk.Label(frame, text="Data > ", bg=self.colors["background"],
                 fg=self.colors["header_info"], font=self.fonts["header_info"]).grid(
            row=0, column=0, padx=22, pady=(22, 0), sticky="nw")

        self.table_name_label = tk.Label(frame, text=self.app.current_table_name or "No Table Selected",
                                         bg=self.colors["background"], fg=self.colors["text"],
                                         font=self.fonts["header_info"])
        self.table_name_label.grid(row=0, column=0, padx=(88, 10), pady=(22, 0), sticky="nw")

        self._setup_settings_section(frame)

    def _setup_settings_section(self, frame: tk.Frame) -> None:
        settings_container = tk.Frame(frame, bg=self.colors["background"])
        settings_container.grid(row=0, column=5, padx=(0, 40), pady=(22, 0), sticky="ne")

        button_s = tk.Button(settings_container, text="S", command=self.show_stats,
                             bg=self.colors["background"], fg=self.colors["text"],
                             font=self.fonts["text"], cursor="hand2")
        button_i = tk.Button(settings_container, text="I", command=self.app.table_io.import_file,
                             bg=self.colors["background"], fg=self.colors["text"],
                             font=self.fonts["text"], cursor="hand2")
        button_e = tk.Button(settings_container, text="E", command=self.app.table_io.export_table,
                             bg=self.colors["background"], fg=self.colors["text"],
                             font=self.fonts["text"], cursor="hand2")
        button_d = tk.Button(settings_container, text="D", command=self.show_datatype_dialog,
                             bg=self.colors["background"], fg=self.colors["text"],
                             font=self.fonts["text"], cursor="hand2")

        button_s.pack(side=tk.LEFT, padx=5)
        button_i.pack(side=tk.LEFT, padx=5)
        button_e.pack(side=tk.LEFT, padx=5)
        button_d.pack(side=tk.LEFT, padx=5)

        def on_button_enter(event):
            event.widget.config(bg=self.colors["button_selected"])

        def on_button_leave(event):
            event.widget.config(bg=self.colors["background"])

        buttons = [button_s, button_i, button_e, button_d]

        for button in buttons:
            button.bind("<Enter>", on_button_enter)
            button.bind("<Leave>", on_button_leave)

    def _setup_lower_section(self, parent: tk.Frame) -> None:
        self.lower_header_frame = create_frame(parent=parent, width=None, bg=self.colors["background"])
        self.lower_header_frame.grid(row=1, column=0, columnspan=5, sticky="ew")

    def show_stats(self):
        """Display stats about the boolean columns in a menu similar to datatype dialog."""
        table_name = self.app.current_table_name
        if not table_name:
            messagebox.showwarning("No Table Selected", "Please select a table to view stats.")
            return
    
        if not self.app.current_sheet:
            messagebox.showwarning("No Data", "No data available to show stats.")
            return
    
        data = self.app.current_sheet.get_sheet_data()
        current_headers = self.app.current_sheet.headers()
        data_types = self.app.data_manager.tables_data[table_name].get("data_types", [])

        while len(data_types) < len(current_headers):
            data_types.append('string')
    
        total_rows = len(data)
        boolean_columns = []
        for col_idx, dtype in enumerate(data_types):
            if dtype == 'boolean':
                header = current_headers[col_idx]
                column_data = [row[col_idx] for row in data]
                true_count = sum(1 for val in column_data if val is True)
                false_count = sum(1 for val in column_data if val is False)
                boolean_columns.append((header, true_count, false_count))

        self.root.option_add('*Menu.disabledForeground', self.colors["text"])
        self.root.option_add('*Menu.font', self.fonts["text"])

        self.stats_menu = tk.Menu(self.root, tearoff=0, bg=self.colors["background"],
                                  fg=self.colors["text"], font=self.fonts["text"])
    
        menu_x = self.root.winfo_pointerx()
        menu_y = self.root.winfo_pointery()

        self.stats_menu.add_command(
            label=f"Total: {total_rows}",
            state='disabled',
            foreground=self.colors["header_info"],
            background=self.colors["background"]
        )

        if boolean_columns:
            for header, true_count, false_count in boolean_columns:
                stats_text = f"{header}: True: {true_count}, False: {false_count}"
                self.stats_menu.add_command(
                    label=stats_text,
                    state='disabled',
                    foreground=self.colors["text"],
                    background=self.colors["background"]
                )
        else:
            pass

        self.stats_menu.post(menu_x, menu_y)

    def update_true_counter(self, count_text: str) -> None:
        pass

    def show_datatype_dialog(self) -> None:
        """Show dropdown menu for changing column data types."""
        table_name = self.app.current_table_name
        if not table_name:
            messagebox.showwarning("No Table Selected", "Please select a table to change datatypes.")
            return

        current_headers = self.app.current_sheet.headers() if self.app.current_sheet else []
        self.app.data_manager.headers[table_name] = current_headers
        self.data_types = self.app.data_manager.tables_data[table_name].get("data_types", []).copy()

        while len(self.data_types) < len(current_headers):
            self.data_types.append('string')

        self.datatype_menu = tk.Menu(self.root, tearoff=0, bg=self.colors["background"],
                                     fg=self.colors["text"], font=self.fonts["text"])

        self.menu_x = self.root.winfo_pointerx()
        self.menu_y = self.root.winfo_pointery()

        self._populate_datatype_menu(current_headers)

        self.datatype_menu.post(self.menu_x, self.menu_y)

    def _populate_datatype_menu(self, headers):
        """Populate the datatype menu with headers and their current types."""
        self.datatype_menu.delete(0, 'end')

        for header in headers:
            header_index = headers.index(header)
            current_type = self.data_types[header_index]
            submenu = tk.Menu(self.datatype_menu, tearoff=0, bg=self.colors["background"],
                              fg=self.colors["text"], font=self.fonts["text"])
            self.datatype_menu.add_cascade(label=f"{header}: {current_type}", menu=submenu)

            for dtype in self.DATA_TYPE_OPTIONS:
                submenu.add_command(
                    label=dtype,
                    command=lambda h=header, t=dtype: self._update_datatype(h, t),
                    background=self.colors["button_selected"] if dtype == current_type
                    else self.colors["background"]
                )

        self.datatype_menu.add_separator()
        self.datatype_menu.add_command(label="Apply Changes",
                                       command=self._apply_changes)

    def _update_datatype(self, header: str, new_type: str) -> None:
        """Update the datatype for a specific header."""
        current_headers = self.app.current_sheet.headers()
        header_index = current_headers.index(header)
        self.data_types[header_index] = new_type

        self._populate_datatype_menu(current_headers)

        self.datatype_menu.post(self.menu_x, self.menu_y)

    def _apply_changes(self) -> None:
        """Apply the datatype changes and update the table."""
        table_name = self.app.current_table_name
        self.app.data_manager.tables_data[table_name]["data_types"] = self.data_types
        self.app.data_manager.save_data()
        self.app.table_display.apply_column_data_types(self.data_types)
        self.app.table_display.process_and_save_current_sheet_data()
        self.app.refresh_table()
        self.datatype_menu.unpost()