Cascading Style Sheets (CSS): was created by World Wide Web Consortium (W3C) as a standard for formatting (HTML) document; what this means is that HTML was really not suitable or best for format for websites anymore.
Before you start defending HTML, just imagine a scenario where you have <FONT COLOR=”GREEN”> inside all your HTML pages in a website of about 100 web pages and tomorrow your boss walk up to you as the webmaster and ask you to please change the font color to black that in about 10 minutes some important clients will be visiting the website and that He just learnt that the GREEN color is not very readable on the white background. I know this might make you sweat real hard, because it means editing each page.
Editing 100 pages in 10 minute is not an easy task and God help you, you forgot to edit one or two pages as this may cost you your job, if your Boss losses the contract.
But with the flexibility of CSS, this task may just require editing only one css file and it will take effect on all the HTML documents that are attached to it. You can see how easy CSS can make your life be.