My menu doesn't look the same in mobiles with Catch box theme and my child theme

Hello, sorry for my english, I'm french. Today, I created a child theme for the theme Catch box. Everything looks great but I have a problem with my menu in mobiles. I took 2 pics to show you my problem. The first is how my site looks like with the theme catch box (It's what I want). The second shows how my site looks like with my child theme. What can I do to have a site like the first with my own child theme ? Thank you so much for your help, Mathilde