Injecting CSS into an existing form

Question

I have a form that is generated and there are no options to format it, so I'm trying to inject some CSS to lay it out a bit nicer. I have been playing around in a PEN at [Pete's Pen](https://codepen.io/pzh20/pen/dyZVrgv) where I've managed to add some section headers, but really want to show form input elements on the same line e,g, first_name next to last_name Company_name next to Trading_as Street_address next to Address2

etc

Is this possible?

Many thanks