Mobile plugin issue

I want when the menu detects mobile device to have a custom width.

you can use the media queries to do this, but this is not managed by the menu itself
check my tutorial
www.joomlack.fr/en/joomla-documentations...e-joomla-for-mobiles

I cannot understand. The entire site is ok, check here

mattkersley.com/responsive/

except the menu. The menu by itself ditects that there is a low resolution screen and changes by itself.

The entire website is ok except the menu.

what you must do for your situation :
1/ Edit the css3megamenu theme in the file
www.inthessaloniki.com/modules/mod_maxim.../css/maximenuhck.php

2/ remove the gradient from ul.maximenuck and give it a fixed width value in px

3/ add the background into your template on "#ja-menu" which is the menu container