HI,

The first place you should look at is how to create skins/themes within Dnn.

There are free skins available in the Dnn Forge, the DnnStore and on Codeplex, just search for Dnn (or dotnetnuke) skins.

There a re also many different kinds of responsive frameworks you can use like Bootstrap which is the favorite for most people and Foundation is another.

The skin by Chris Hammond uses Bootstrap and is open source called Hammerflex and can be found here, The DnnFoundation skin which is also open source uses Zurb foundation, this skin can be found here.

Have look to see how they work, install them and play about with them.

Hope this helps,

Regards,

Geoff