Answer:
People walk in and out of me. They push me and I follow. When they walk out on me I close up and I stay waiting for the next person to walk into my life when I have a more open mind
Lighter than what I am made of, more of me is hidden than is seen. What am I?
They come at night without being called and are lost in the day without being stolen. What are they?
I can be simple or I can be complex. I can be found in this riddle or in everyday life. I can be shapes or even colors.
I have roots that no one sees and I am taller than trees. Up, up I go, but never do I grow. What am I?
It has no top or bottom, but it can hold flesh, bones, and blood all at the same time.