Load more tiles in small div

I am trying to achieve what foursquare did with their UI! Offset center of map to the left https://foursquare.com/.

I have discovered how they did one part but can't implement the second part.

The first part was to load the map inside a small div (the one that will contain the markers), then with an overflow:visible, other tiles would fill the parent div which has width:100%.

The problem I am encountering right now is that only few tiles are showed when I do the overflow:visible.

My question is: how can I load more tiles inside of small div ?

The following picture explains how the tiles don't fill the whole container Thank you.