HTML Element Hierarchy Needed

I would like to try and design new styles FROM SCRATCH for the default Vanilla theme, but I'm finding it a bit daunting. I find that the best way to design a good style sheet is to start by really getting to know the HTML hierarchy of the page you are trying to format. Unfortunately (or fortunately, depends how you look at it), each of the few CSS documents in Vanilla is used by several possible html pages which are output by the php code. This is where I'm getting stuck. Take, for instance, the "people" page - which seems to be used for signing in. Even for signing in, there are actually several possible pages (depending on whether a warning is being shown or not, for instance). It is difficult to design a totally different layout, unless I can have a really good idea of what the maximum number of items is going to be on that page - and what the "id"s and "classes" of all of these items are. I was wondering, if anywhere there is some sort of 'schematic diagram' or the full HTML element hierarchy of the pages outputted by Vanilla. If not, what pages should we be looking at if we want to design, let's say, an entirely new style, FROM SCRATCH, for the default Vanilla theme?