title: What is the precise explanation of box-shadow and -moz-box-shadow in CSS?
body: <p>I find the explanations of CSS's <code>box-shadow</code> and <code>-moz-box-shadown</code> somewhat imprecise.</p>
  <p><a href="http://www.w3.org/TR/2010/WD-css3-background-20100612/#the-box-shadow" rel="nofollow noreferrer">http://www.w3.org/TR/2010/WD-css3-background-20100612/#the-box-shadow</a></p>
  <blockquote>
  <p>The third length is a blur distance.
  Negative values are not allowed. If
  the blur value is zero, the shadow's
  edge is sharp. Otherwise, the larger
  the value, the more the shadow's edge
  is blurred.</p>
  <p>The fourth
  length is a spread distance. Positive
  values cause the shadow shape to
  expand in all directions by the
  specified radius. Negative values
  cause the shadow shape to contract.</p>
  </blockquote>
  <p>Is it true that the fourth length will use the same color (the darkest shade), and repeat that for the specified width?  So it won't be smoothly blurring out?</p>
  <p>Can it achieving specifying the rate of blurring or the rate of fading out...?</p>
  <p>Does someone know very precisely how they exactly work?</p>