out.css

header nav {
  -webkit-box-shadow: 0px 0px 5px rgba(0, 0, 0, 0.4);
  -moz-box-shadow: 0px 0px 5px rgba(0, 0, 0, 0.4);
  box-shadow: 0px 0px 5px rgba(0, 0, 0, 0.4); }
  html.ie8 header nav, html.ie7 header nav, html.ie6 header nav {
    border: solid 1px #cccccc; }

shadow.sass

=shadow($color: hsla(0, 0%, 0%, 0.4))
  :-webkit-box-shadow 0px 0px 5px $color
  :-moz-box-shadow 0px 0px 5px $color
  :box-shadow 0px 0px 5px $color
  html.ie8 &, html.ie7 &, html.ie6 &
    :border solid 1px #ccc   // fine, just border it with gray

// and then usable on any random element:
header
  nav
    +shadow

shadow.styl

box-shadow()
  -webkit-box-shadow arguments
  -moz-box-shadow arguments
  box-shadow arguments
       
header
  nav
    box-shadow 1px 1px 3px #555