How do I get my comforter to stay in place inside the duvet cover?

I have a king-size quilt and I bought a quilt king size cover. But the Comforter insists move especially in the corners.

I made button holes on the bottom of the quilt. And I sewed the buttons on the corners cozy room. This keeps the dildo in his fall into the quilt. And the questions do not miss or scratch scratch!

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