Internet Explorer 4.x

Microsoft greatly extended CSS compatibility within the initial 4.x version of Internet Explorer. This version of Internet Explorer was the first to show that a major browser vendor was serious about implementing CSS.

This version of Internet Explorer was not without its drawbacks, however. While it supported much of the background, border, font, margin, list and padding CSS element families at least partially, it could not support a number of other elements, such as display or clear/float in the Macintosh version at all. There were also some minor variances worth noting in the ways the browser implemented the same CSS elements across different operating systems. Problems implementing the text-align property have been noted, as have more general problems when implementing some basic CSS functions, such as containment, inheritance and dealing with certain length units.

This version of Internet Explorer has subsequently been superceded by versions 5.x and 6.x, and the vast majority of Internet Explorer users now use one of these later releases. However, it is worthwhile keeping its limitations in mind for those few users who may still be using it.

Microsoft's tendency to start adding their own browser-specific CSS properties began with this release of Internet Explorer. The filter property was added to this version, enabling Web authors to add a number of transitioning effects . Compared to later versions of the browser, this was a relatively minor addition, but arguably started a trend towards adding fresh browser-specific properties in future versions of Internet Explorer.

Another interesting development with this version of the browser was that it implemented — at least partially — some positioning properties (like top, left and vertical-align) which were being considered at the time for inclusion for the CSS2 specification, which was in a draft status at the time. Microsoft was truly looking forward with this development, though it would take version 5.5 before CSS2 properties were substantially supported.