Evenly space items in grid?

[Emiliano Parizzi]

I'm not being able to distribute items evenly across the grid. What I mean is, how to make it so both the vertical and horizontal margin between items is the same.

In this codepen (http://codepen.io/emzero/pen/eZzPQj) you can see the horizontal margin depends on the width of the window. I'd like items to have a specific margin between them and center the whole grid in its container if necessary.

[Attila Beregszaszi]

I'm not sure what you mean but having an equal margin between columns and items is a simple CSS related question, see http://codepen.io/anon/pen/PNGJeP