Collapse Megamenu on Mobile - Impulse Theme

[wickedbride]

Good evening, everyone - 

I'm trying to collapse the megamenu on mobile only for my in-process site redesign. On mobile, it displays all of the link branches, and I'd like to tidy it up and have it collapsed by default. I found a previous solution:

https://community.shopify.com/c/shopify-design/impulse-theme-stop-children-auto-displaying-on-menu-d...

But for the life of me, I've tried putting this code in everywhere (theme.liquid, header files, etc.) and it's not working. I'm new to the Impulse theme and honestly a bit disappointed on all the custom coding I'm having to do (but overall love a bunch of the features). 

Here's a preview link, it will eventually expire: https://00cnb7ifxu52rjr4-34171617415.shopifypreview.com

I'd also love to make the links blue to match the desktop nav links - I fixed this on desktop but can't figure out mobile. 

Thanks!

[wickedbride]

Hello - yes, I've tried multiple custom CSS coding, but can't seem to figure out which tag/element is controlling these features, so nothing I've tried has worked.