Mini-menu toggle width

Hi

I use Untitled Theme for my professional site https://www.jordipratsolle.com. I like to play/hack there, and try to learn a little about wordpress. Some time ago I created a child theme and started changing the look of the theme, more or less successfully.

Now I’m having problems to control the mini-menu toggle. To change the width at which triggers the mini-menu, I modified the “Media queries for responsive design” css, created a new set of rules, but there must be something hidden somewhere, as the menu keeps ignoring my rules (are mostly working, but not for the menu toggle), and keeps triggering at 600px width.

I’ve found some documentation about toggling the menu, but only related to other themes (Twenty Twelve, p.ex.), nothing specific to Untitled. Is that behavior defined somewhere else in my theme? maybe hidden in a .php file? What I’m doing wrong?

Any help would be appreciated.