title: CSS3 Box shadow size – percent units?
body: <p>I'm working on a project that needs to use CSS3 box-shadow property.
  That's fine, but I have found out that spread size of shadow can't be set to a percentage of parent object.</p>
  
  <p>I fully understand that box-shadow is not additive, thus it doesn't take the size of a parent as a reference.</p>
  
  <p>But given the fact that I need to have a fully responsive site with objects scaling fluidly (not only on breakpoints), but this also poses a problem – I can set shadow to spread property only in absolute units (em or px).</p>
  
  <p>Is there any solution to this? I thought about using inner container (for content) within container (for "shadow" – it's without blur), but this creates another problem – vertical centering of inner container.</p>
  
  <p>Any solution? No jQuery please, just pure CSS.</p>