Can't allign text

When I make a flex box vertical and select center and then i write something in it, the first line gets centered perfectly fine. Then I write enough text to get to a second row and suddenly the centered text becomes normal and starts from the left as all text would.
I have tried a lot and find it really strange, originally I used left/right margin but no top/bottom margin. After that did not work I selected no margin and I had the same issue.


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