Hi @Herrmann
By looking at your HTML, I can deduct that you are using menu field for your nav. You can give your own CSS in the same class and overwrite the default styles. If you want to completely remove this class then you can use JavaScript.
{% require_js %}
<script>
const list= document.querySelector('.hs-item-has-children ul');list.classList.remove('hs-menu-children-wrapper');
</script>
{% end_require_js %}
You can add this script in your header module or in header partial template.
I hope this will help you out. Please mark it as Solution Accepted and upvote to help another Community member.
Thanks!