How do I create a separate style for the sub-navigation in the Wells template?

Site URL: https://cylinder-haddock-nfkd.squarespace.com

Hello,

I'd like to have a separate style for the sub navigation items in the expandable side menu for my site, which is built using the Wells template.

At the moment, my navigation looks like image A, where the main and sub nav fonts are identical:

But, I'd like it to look more like image B, where the sizes, weights and colours of the main and sub nav fonts are different:

As a bonus, I'd like to be able to adjust the indentation of the sub nav items, if possible.

Any advice would be much appreciated!

Thanks,
Greg

UPDATE: I've managed to customise the fonts (see screenshot with code, below, for anyone else who is looking for a similar solution) but I can't seem to alter the colour (again, see screenshot with code, where the colour is meant to be specified):

I'd be grateful for any help with the above problem.

Thanks again.

Hi. Do you still need help on this?

If yes, can you setup password & share url again? Your site is private.