Unfortunately, CSS exam is all about your analytical skills where you have to opt more generalistic approach. you don't need any technical knowledge neither mere objective knowledge. you need to have an ability to mould the available facts in your favour to prove your point of argument at least for the paper of Essay. Secondly, your writing skills and language expression must be up to the mark, and there is no exception to that. Lastly, you need to have luck on your side as well to get you through this exam, keeping in mind that enormous amount of hard work and motivation(could be anything) are your basic tools.