Marvin responsive issues

Hello And First of all thank you for providing this theme for free it’s very fun to work with

I cannot provide page details as I have it on my local server
My problem is the following :
While creating a new page I realized the following:
The container was a little too small to use and the margin was too high so the left and right side had big blanks. Thus I decided with custom CSS to make the margin to – 40% or -100px and it solved the problem I can now use the left and right side a little bit more. I want to add some navigation menu etc.
But ! When I drag the site together into mobile view the pre written test text goes beyond The horizon on the right side
It’s not responsive anymore. How can I fix this problem ? How do I add container in full width of the page without having responsive problems ?
I appreciate the help
Desory