Overriding CSS properties that don't have default values

Question

Is it possible in CSS to override a property if that property doesn\'t have a default value?

For example, say your primary stylesheet defines a border for a particular

Answer 1

Every CSS property has Browser dependent default value so there is no such thing as CSS property without default value.

As BoltClock stated, initial is best choice.

Here is some specs about it:

http://www.w3.org/TR/css3-cascade/

EDIT:

Before jmbertucci's comment I did not think how I have done this always,

By using CSS reset you can define your own default values which does not depend on used browser. If you define left: 10px; in your own reset.css then you can use that same value when you need it to fall back to default.

For example I often look for font-sizes from my reset.css and use them to do height calculations that depends on text height.

And if using PHP or some other preprocessing you can always use that for CSS files too:

div {
    top: 100px;
    
}