It doesn’t always work like the other browsers. Here is something to try out:

.parent {
    display: flex;
    align-items: center;
    justify-content: center;
    .obj{
      display: flex;
      flex-direction: column;
      width: 100%;
    }
  }

More info: https://philipwalton.github.io/solved-by-flexbox/demos/vertical-centering/