@pitrek121, you are so fabulous, you drew the chair almost looks exactly the same although you didn't see the chair.
Actually I didn't draw it outside the box at the beginning, because the chair back has an arc so I extended the box a bit, and then filled it with color, so it might seem to have gone outside the box. Anyway, thank you very much, @pitrek121! Your answer is very specific and very helpful to me.
Also, thank you, @haight_nicholas, I did not carefully observe the angle of the chair. In fact, it has five legs. thank you very much for your reminder.
Thank you, @chiara.arcidiaco for your reply. Here is the chair photo. I should include it at the beginning. Please ignore the messy background.
Finally: I didn't intend to draw such a difficult object on purpose. Thank you all for your help.