How do i lock my responsive html for a certain screen size only?

[workman60405]

Hey i need to lock my viewport somehow to this(For both Desktop, Tablet and phone): http://i.imgur.com/V0zzKej.png
From this: http://i.imgur.com/n78XY1g.png
My HTML and CSS code is here: http://pastebin.com/mbwhRpDY
Thank you in advance <3