Thank you for the clarification, Fay. I must make it a habit of checking w3school more, it's a very useful resource.
Yesterday I added your selectors to a stylesheet I was already using and it worked. However, what confuses me is that I've typed the same selectors into 'Styles' but when I view it makes no difference to the page.
Also, am I correct in thinking that I can type a whole shylesheet into 'Styles' and that would work the same? Only ask because I've tried it and it makes no difference to the page.
Finally, one last query. What do I actually add to a style/stylesheet in order to customize the menu that appears in the top black strip of the bootstrap template?
Thanks for your valued help.