style(rxApp): Add styles and documentation for Account Info box

Closes #555.

See https://jira.rax.io/browse/EOD-2
This same value is used in our tabs: https://github.com/rackerlabs/encore-ui/search?utf8=%E2%9C%93&q=4480c1

It's a little extra work, but do you mind moving this value into the vars.less file and replacing the instances here and in tabs.less?

![](http://media.giphy.com/media/I1nwVpCaB4k36/giphy.gif)