I'm confused about the part of the following in red.
For example, it does not really matter if you cross your legs or use a backrest, or if you really prefer a posture involving a Hello Kitty soft doll on your head. As long as you can remain alert and relaxed, that is good.
Does this refer to a posture "in which you put a Hello Kitty soft doll on your head"? Is this a kind of humorous expression?
I can only suppose that it means standing up straight like you would have something on your head (in this case - Hello Kitty doll) that limits your movements.
It sounds a bit humorous.
Thank you for the answer.