That was then. Today, less than 1% of users are stuck with Netscape 4.x, and barely 1% use Internet Explorer 5.x or older. The overwhelming majority have Internet Explorer 6.x, Firefox, or another modern web browser.
Using CSS instead of tables offers many advantages. Most importantly, CSS allows you to separate all of your layout into a single site-wide .css file, if desired, leaving only the actual content in your HTML files. That keeps your HTML simple... which makes it easy for Google and other search engines to index correctly. It also makes your site highly accessible to visually impaired users. Finally, CSS saves bandwidth and speeds up your site, because the .css file for the site only has to be downloaded once. Compare that with hundreds of pages full of ugly table code.
The main drawback of CSS is that, even today, you'll still need to test your page carefully in both Firefox and Internet Explorer and make adjustments until both browsers work smoothly. That has always been the case, but table-based page designs do produce more consistent results between browsers.
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