Bootstrap is a free front-end framework for faster and easier web development.Bootstrap also gives you the ability to easily create responsive designs.
Bootstrap includes HTML and CSS based design templates for typography, forms, buttons, tables, navigation, modals, image carousels and many other, as well as optional JavaScript plugins.
Responsive DNN is using Telerik ajax menu for DNN, which proves that a simple DNN design CSS skinning is good to produce a pack that can apply to your DNN site.
For your site map to work best with smartphones, tablets, desktops - it is best to have 6 parent tabs as the menu puts the first 3 on the left of the logo and any more tabs on the right. Therefore you need to ensure that you have a nice balance of tab numbers and tab names. 3+3 will work great. If you have more than 6 pleas place the links within the pages you create or as child tabs.