## The Active CSS Definition

The most important thing to know about TopStyle Lite is how the Active CSS Definition works. To change the active CSS definition, simply select from the CSS definition dropdown shown below:
The active CSS definition determines which properties and values are displayed in the Style Inspector and Style Insight. For example, if you choose "Internet Explorer 3" from this dropdown, only properties and values that are understood by Microsoft Internet Explorer 3.x will be displayed.

To help you quickly locate problems, any properties in the current style sheet that aren't supported by the active CSS definition will be color-coded red. If ensuring the validity of your style sheets is important to you, make sure to check out the full version of TopStyle. The full version includes a powerful style checker than validates your style sheets against multiple CSS definitions, pointing out errors in both properties and values as well as alerting you to bugs in popular browsers that may impact your style sheet. In addition, the full version can even pass the current style sheet to the W3C's online CSS validator!

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