NavLinks, FooterLinks, NavLink and FooterLink should be using `styled`.

Currently NavLinks, FooterLinks, NavLink and FooterLink styles can all be removed by passing in `styles={}` , obviously, breaking the way they are displayed.

Other components are using the function `styled()`, e.g.
```
const BarStyled = styled(Bar)(
({ theme }) => ({
backgroundColor: theme.vars.palette.primary.light
})
);
```