This div has style="width: 80%; border: solid red;"
This div has style="width: 80%; border: solid blue;"
This div has style="width: 80%; border: solid silver;"


The silver div position is now absolute.

When the silver-bordered div is absolutely positioned, it should be at least as wide as the red-bordered div. (Its width depends on how exactly the user agent implements the "initial containing block": the "initial containing block" should be at least as large as, as wide as the document root element.

References:

HTML 4.01 Strict compliant CSS compliant