axa-fieldset css neagtive margin question

[MarekLacoAXA]

Pls. explain the reason for negative top margin of axa-fieldset root and its neagtion with positive top margin in its children.
What is this good for?
It complicates my spacing of axa-fieldsets siblings.

Thx!

https://github.com/axa-ch-webhub-cloud/pattern-library/blame/04d7e0f227f85d7b39eb0a6bfa9911076027e924/src/components/10-atoms/fieldset/index.scss#L17

    margin-top: -$fieldset-vertical-margin;

    > * {
      margin-top: $fieldset-vertical-margin;
    }