So far, I haven't mentioned text styles. If I add a text style definition to the 'body' style, it will pass down to all the other boxes by 'inheritance'. If we add text style definitions to any of the boxes, they over-ride the inherited styles. Think of the body text style definition (if you provide one) as being the default for everything on the page - unless you tell it otherwise. I prefer to put a really oddball text style definition (say, red Courier) in the 'body' while I'm building the page just to check that everything is more appropriately defined - then I remove it before publishing.
The other way to define text styles is to enclose the text itself inside its own class or span div. Where you have more than one text style inside a box, you will need to do this anyway.