CSS is too superficial for this purpose. It is a styling language to help with layout and look and feel.
What you want is an end to end solution using Rails to calculate, summarise and serialise your data, Ember JavaScript to receive the data and present it nicely on a route and CSS to style it as required. You could even use the D3 library to make a particularly nice visualisation.
Take a look at my Word Cloud or Network Vis Plugins that do exactly all this. Modify them to suit your requirement.