How to make an existing website responsive using zengrids? i'm creating a website using drupal 7, zen theme with some other modules, like superfish menu for example, for now the website is empty, i'm wondering how to make the website responsive from now ? Can i just (from my starterkit theme) access to the css (or create my own) that contains some media queries and it will work ? or zengrids is a best solution ?
I have found the Superfish module plays well with the Zen theme. By default, it will toggle wide dropdown menus to accordion style menus at 768px. 

The superfish library includes sass and css template files you can drop into your theme's scss or css folders.

I am using a custom theme based on Zen 7x-6x starterkit.