Menu bar not fitting into screen size

Hi,

I contacted the theme I am using as the Menu Bar is extending outside of the screen when open however I received this message:

‘Thank CSS in embed directly is code from plugin https://wordpress.org/plugins/widgetize-navigation-menu/, so you need to contact their support on this. It is taking full width of the screen, it need to take the wrapper width.’

Can you help please?

Thanks,

Dan