Why is the size and operation of flex-box not quite accurate on Android?

Question

Android

Hello!
When you try to center the block using flex-box, it seems to be in the center, but a little lower.
And the markup itself, it seems to me, is sometimes a little bit not quite correct.

<meta name="viewport" content="width=device-width, initial-scale=1.0">

Maybe I entered the wrong values?
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