Why tabs don't behave like normal elements with flex box

why tabs don’t behave the way it should with flex box. I provided a read-only link. I countered similar problem with grid. if it is because of some pre-set css properties, how can I turn them off?

https://preview.webflow.com/preview/mohamads-awesome-site-4e6d24?utm_medium=preview_link&utm_source=dashboard&utm_content=mohamads-awesome-site-4e6d24&preview=5c3491d359e6ed26a9e43a3067cc9aa8&workflow=preview


Here is my site Read-Only: LINK
(how to share your site Read-Only link)