Wood will expand and contract across the grain, and a wide panel made of solid wood could change width by a half of an inch, warping the door frame. By allowing the wood panel to float, it can expand and contract without damaging the door.
Put trimmed and cleaned green beans in the steamer basket, set over the boiling water, cover, and steam until tender to the bite, 3 to 5 minutes (depending, again, on how crisp or tender you like your green beans).
The cooking time of green beans can vary quite a bit. It will be at least 10-15 min, sometimes it can go up to 30 minutes. I advise you to cook them for about 10 minutes and taste one. Do so every two-three minutes until you have them a tiny bit too hard for your taste. After that, you will fry the beans (for example with oil/butter and onion) which will make them a bit softer, as you like them.