It is fairly a common UX practice to highlight the currently active page in the website’s navigation. It helps users to easily find out their current location in the website.
Similar to React Router’s <NavLink/> component, Gatsby’s <Link/> component has built in attributes to allow developer to style currently active link in the navigation.
Add CSS to <Link/> Component
<Link
to="/contact/"
activeStyle={{
color: "#000",
fontWeight: 600
}}
>
Contact
</Link>
OR
Add CSS Class to <Link/> Component
<Link
to="/contact/"
activeClassName="active"
>
Contact
</Link>