Increase size of Banner font in Mobile Only

Hi, I'm trying to increase the Banner Font in my mobile view only. It's very, very, small in mobile view, you can barely see it, but looks fine in desktop view.

I read a few similar forum Q&A's and tried this code, but I must be doing something wrong because nothing happens:

@media only screen and (max-width: 700px)

{#collection-5de407418ca23e2f1db0bc3a {font size: 90px ! important;} }
 

I used the chrome Block ID extension but the banner doesn't pick up a block #, only a collection #

Can someone let me know what I might be doing wrong here?

Thanks!