In early HTML, stylistic elements of a page were specified using tag attributes.
For example, the background color of a page could be specified like this:
<BODY BGCOLOR="#FFFFFF">
...
</BODY>
Or the color of some text might be changed like this
<FONT COLOR="#FF0000">color</FONT>
Unfortunately, there are a few problems with this approach:
It clutters a document with specific formatting information.
Excessive formatting increases the size of a document (if you care about performance).
Makes documents harder to maintain and modify (If you want to
modify a certain stylistic element, you may have edit every occurrence
within a page).