How to center blocks inside a div?

Question

css

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Answer 1

.parent-div {
    display: grid;
    place-items: center;
}

Answer 2

align-items: center centers vertically, if that's what you mean

Answer 3

If you are talking about Boostrap, then the mx-auto class aligns horizontally, and my-auto aligns vertically

Answer 4

display:flex;
justify-content: center; or align-items: center;
We don't know what you need