如何在 python tkinter 中使用 ttk 组件？

#这里调用了Checkbutton控件与ttk结合一起使用。
from tkinter import *
from tkinter.messagebox import *
# 新建窗体
root = Tk()
root.geometry("450x100")
root.title("CheckButton控件")
#Label标签
Label01 = Label(root,text = "请选择你去过的城市")
Label01.grid(row = 0,column = 0,padx = 0,pady = 20)
city_list = ["北京","上海","广州","深圳","南京"]
# 用一组值存储选中哪些
is_check_list = []
# 通过循环展示
for city in city_list:
    is_check_list.append(IntVar())
    CheckButton01 = Checkbutton(root,text=city,variable = is_check_list[-1])    # 为啥是-1
    CheckButton01.grid(row = 0,column = len(is_check_list),padx = 5,pady = 5)
# sel函数
def sel():
    all_select = ""
    for i in range(0,len(is_check_list)):
        if is_check_list[i].get() == 1:
            all_select += city_list[i] + " "
    Label_select["text"] = "所选城市为:"+all_select
# 添加一个Button
Button01 = Button(root,text = "确认选择",command = sel)
Button01.grid(row = 1,column = 0,padx = 5,pady = 5)
# 添加一个Label标签，用于展示显示后的结果
Label_select = Label(root,text = "")
Label_select.grid(row = 1,column = 1,columnspan = 5)
# 加载
root.mainloop()