I am in 
with the new full screen composer mode.
However, I do not understand why it is missing the “Post button”. If I am done editing, I need to first exit the full screen mode in order to post it. Note that the status bar with “saved” status at the bottom is there anyway, so why not expose the button as well?
The reasoning for this decision was already explained in the middle of this post.
No, you don’t. Press Ctrl+Enter.
Hovering your mouse pointer (if on a mouse capable device) over the reply button offers this hint as well:
我们能重新讨论一下这个问题吗？今天有一位用户因此卡住了，直到他发给我一张截图我才明白是怎么回事。虽然当初解释这一决策初衷的原始帖子已经不见了，但在我看来，在全屏模式下移除按钮是一种极差的用户体验。普通用户不会知道要使用 Ctrl+Enter。我想我可以把全屏按钮隐藏起来……
请看这里