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HTML 

              
                <div class='container lead'>
  <h1>Isolating Box Shadows</h1>	
  <h2>A Simple & Often Misunderstood CSS Fundamental</h2>
  <p>To isolate a single shadow we apply a negative spread and offset in the desired direction, then add a blur radius of equal distance to compensate. For inset shadows, the spread remains constant but we apply an offset in the opposite (-ve) direction. For multiple sides/shadows, simply combine any of the desired single-side rules into a comma separated list.</p>
</div>

<div class='container'>
  <div class="box top"></div>
  <div class="box right"></div>
  <div class="box bottom"></div>
  <div class="box left"></div>
  <div class="box all"></div>
</div>

<div class='container'>
  <div class="box inset-top"></div>
  <div class="box inset-right"></div>
  <div class="box inset-bottom"></div>
  <div class="box inset-left"></div>
  <div class="box inset-all"></div>
</div>

<div class='container'>
  <div class="box top-bottom"></div>
  <div class="box left-right"></div>
  <div class="box inset-top-bottom"></div>
  <div class="box inset-left-right"></div>
</div>
!

CSS 

              
                $w: 15px; // shadow size
$color: #2C3E50;
$box_w: 4 * 40px;
$box_h: 3 * 40px;
$box-color: #16A085;
$label-color: #fff;
$bgcolor: #1ABC9C;
$text-color: #fff;



//--------------------------------------------------------------------
// Here's the important stuff, 
// Click the 'view compiled' button if you don't know SASS/SCSS
//--------------------------------------------------------------------


/*  CSS Spec:  | style | offset-x | offset-y | blur-radius | spread-radius | color */
$shadows: (               
	top          :            0          (-$w)       $w            (-$w)       $color,
  right        :            $w         0           $w            (-$w)       $color,
  bottom       :            0          $w          $w            (-$w)       $color,
  left         :            (-$w)      0           $w            (-$w)       $color,
  all          :            0          0           $w                        $color,
  inset-top    : inset      0          $w          $w            (-$w)       $color,
  inset-right  : inset      (-$w)      0           $w            (-$w)       $color,
  inset-bottom : inset      0          (-$w)       $w            (-$w)       $color,
  inset-left   : inset      $w         0           $w            (-$w)       $color,
  inset-all    : inset      0          0           $w                        $color,

  /* You may also combine and comma separate any shadows from above */
  left-right       : (       (-$w) 0     $w (-$w) $color,       $w    0     $w (-$w) $color),
  top-bottom       : (       0     (-$w) $w (-$w) $color,       0     $w    $w (-$w) $color),
  inset-left-right : (inset  $w    0     $w (-$w) $color, inset (-$w) 0     $w (-$w) $color),
  inset-top-bottom : (inset  0     $w    $w (-$w) $color, inset 0     (-$w) $w (-$w) $color),
);
  
// Loop and create style
@each $k, $v in $shadows {
  .#{$k} {box-shadow:$v;}
}


//--------------------------------------------------------------------
// Ignore me I'm just eye candy
//--------------------------------------------------------------------
@import url(https://fonts.googleapis.com/css?family=Slabo+27px);

body {
  background-color: $bgcolor ;
  color:$text-color;
  letter-spacing: 1px;
  font: 1em 'Slabo 27px', serif;
  
  h1 { margin:20px; font-size:3.5em; letter-spacing:5px; color: #006666; text-align:center; font-weight:bold;}
  h2 { margin:20px; font-size:1.5em; color: #006666; text-align:center;}
  p  { margin:20px; font-size:1.1em; }
  .container {
    text-align:center;
    clear:both;
    margin:auto;
    max-width: 6 * $box_w;
    &.lead {
      max-width:710px;
      text-align:justify;
    }
  }
  
  .box {
    display:inline-block;
    height: $box_h;
    width: $box_w;
    margin: 30px 10px;
    position:relative;
    background: $box-color;

    &:after {
      color:$label-color;
      position:absolute;
      top:0;
      left:0;
      right:0;
      bottom:0;
      line-height: $box_h;
      color:#eee;
      content: attr(class) " ";
    }
  }
}
!

JS
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