From http://www.w3schools.com (Copyright Refsnes Data)

Web Quality - Style Sheets

Using Style Sheets is important to web page quality.

Don't Use the Font Tag

The text size used to display information on a web page should be set using CSS (Cascading Style Sheets). Do not use the HTML tag.

Using the tag will increase the size of your document, and give you a nightmare every time you decide to change your standard text size.

Think of the following example:

One day you decide to change all the headers in your web to another color and another size. With CSS you can change the color and size attributes by rewriting one line of code. If you have used the tag, you will have to edit the tag for all the headers in all the pages of your web.

Using styles instead of tags makes it much easier to give all the pages of your web a high quality and consistent look.

Don't Use Fixed Sizes

Never use fixed size values. Always use relative size values.

The most important reason for this advice is that fixed sizes can not be resized by the browser.

Your visitors will have different equipment (monitors), different viewing conditions (light), and possible disabilities (poor eyesight).

Setting your default text size to 100% (or medium), your main headers to 140% (or x-large), your sub headers to 120% (or large), as an example, will make it possible for your reader to resize your pages to their best fit.

Want to see how it works? Select view in your browsers menu, and change the text size for this page.

Adjusting the text size of a web page also changes the amount of text that will fit on a printed page.

Don't Use a Small Default Font Size

Some web sites use a small text size just to "squeeze" more text into each page, or to make the page more "stylish".

Again, visitors with different equipment, viewing conditions, and disabilities (and sometimes most people) will have difficulties reading the text.

Don't force your visitors to enlarge the text size every time they visit your site.

Always Use a Background Color

Most web pages use colors for different text elements. Both headers and links are often in a different color from the body text.

As a web designer, you should be aware of the fact that your visitors are able to change their default color preferences.

If you define colors for your web elements (like header and links), you should also define the background color.

If you don't define a background color, your web site might end up with some very bad combination of colors (like light red headers on a red background, or even worse, black text on a black background)

If you don't specify a background color, your text might be invisible.