Hi Deb,
I don't see very many people jumping in, so I will try.
A theme is a Fromt page/Microsoft word creation. It is an easy way to set
the look of your siteor document. Colors, graphics are all set up. You can
edit a theme and save them with new names. You can change the graphics,
fonts or colors.
CSS Style sheets are a list of things like fonts, colors, behaviors like
underlining, etc. A HTML page refers to this and sets the page to use the
styles listed. If you want to change your website, you can just change a
line or two in the style sheet and all the pages that use that sheet will be
changed. (easy to update)
A Template is a web page or web site that is used as a pattern. You just
fill in the blanks with your information and save it with a new name. The
original is not changed so it can be used again. You can make your own
template or buy a premade one. I am not sure what a regular style sheet is.
I think it is from the publishing world, letting printers and writers know
how to set up their work, so everyone would be the same.
SandyB