Behavior--expression in CSS

IE5 and its later versions support the use of expression in CSS to correlate CSS properties with JavaScript scripts, where CSS properties can be intrinsic attributes or custom attributes. This means that the CSS property can be followed by a JavaScript expression, and the value of the CSS property equals the result of the JavaScript expression calculation. You can directly reference the properties and methods of the element itself in an expression, or you can use other browser objects. The expression is as if it were in a member function of the element. Do you feel the text above is a bit obscure? No matter, you just need to know: we can use expression to write JavaScript script in the CSS file, through it to achieve some very convenient functions and effects.
<style type= "Text/css" >

#myDiv {
Position:absolute;
width:100px;
height:100px;
Background: #c00;
Left:expression (document.body.offsetwidth-180 "px");
Top:expression (Document.body.offsetHeight- -80 "px");
Text-align:center;
line-height:90px;
Color: #fff;
}

</style>

Behavior--expression in CSS