Postage stamp

            
              $mark-w: 21rem;
$mark-h: 12rem;

$perc: 46%;
$size: 2.3rem;
$offset: 1rem;
$color: white;
$transparent: transparentize($color, 1);

$waves-size: $size*.5;
$waves-perc: 25.5%;
$waves-color: transparentize($color, .8);
$waves-step: 3;

$bgcolor: darken(powderblue, 7%);

@import url(https://fonts.googleapis.com/css?family=Spicy+Rice);

HTML, BODY {
  height: 100%;
  }

BODY {
  background: 
    radial-gradient( circle at $waves-size*2.5,
      $transparent $waves-perc,
      $waves-color $waves-perc, $waves-color $waves-perc + $waves-step,
      $transparent $waves-perc + $waves-step
      ) 0 0,
    radial-gradient( circle at 0 - $waves-size*.5,
      $transparent $waves-perc,
      $waves-color $waves-perc, $waves-color $waves-perc + $waves-step,
      $transparent $waves-perc + $waves-step
      ) 0 $waves-size,
    
    radial-gradient( circle at $waves-size*2.5,
      $transparent $waves-perc,
      $waves-color $waves-perc, $waves-color $waves-perc + $waves-step,
      $transparent $waves-perc + $waves-step
      ) $waves-size/2 0,
    radial-gradient( circle at 0 - $waves-size*.5,
      $transparent $waves-perc,
      $waves-color $waves-perc, $waves-color $waves-perc + $waves-step,
      $transparent $waves-perc + $waves-step
      ) $waves-size/2 $waves-size,
    
    radial-gradient( circle at $waves-size*2.5,
      $transparent $waves-perc,
      $waves-color $waves-perc, $waves-color $waves-perc + $waves-step,
      $transparent $waves-perc + $waves-step
      ) $waves-size 0,
    radial-gradient( circle at 0 - $waves-size*.5,
      $transparent $waves-perc,
      $waves-color $waves-perc, $waves-color $waves-perc + $waves-step,
      $transparent $waves-perc + $waves-step
      ) $waves-size $waves-size,
    
    radial-gradient( circle at $waves-size*2.5,
      $transparent $waves-perc,
      $waves-color $waves-perc, $waves-color $waves-perc + $waves-step,
      $transparent $waves-perc + $waves-step
      ) $waves-size/2*3 0,
    radial-gradient( circle at 0 - $waves-size*.5,
      $transparent $waves-perc,
      $waves-color $waves-perc, $waves-color $waves-perc + $waves-step,
      $transparent $waves-perc + $waves-step
      ) $waves-size/2*3 $waves-size
    ;
  background-size: $waves-size*2 $waves-size*2;
  background-color: $bgcolor;
  }

H1 {
  position: absolute;
  margin: auto;
  top: 1em;
  bottom: 1em;
  left: 1em;
  right: 1em;
  width: $mark-w;
  height: $mark-h;
  line-height: $mark-h;
  background-color: white;
  text-align: center;
  font-size: 2.2em;
  letter-spacing: .05em;
  font-family: 'Spicy Rice', cursive;
  color: $bgcolor;
}
.hello {
  display: inline-block;
  vertical-align: middle;
  height: 3.2em;
  line-height: 3.2em;
  padding: 0 1rem;
  background: $bgcolor;
  border-radius: 50%;
  color: $color;
}

H1:before,
H1:after {
  content: '';
  position: absolute;
  z-index: -1;
  }
H1:before {
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  box-shadow: 0 0 3rem darken($bgcolor, 35%);
}
H1:after {
  top: -$offset;
  right: -$offset;
  bottom: -$offset;
  left: -$offset;
  background: 
    linear-gradient(
      $color, $color
    ) no-repeat left top,
    linear-gradient(
      $color, $color
    ) no-repeat right top,
    linear-gradient(
      $color, $color
    ) no-repeat left bottom,
    linear-gradient(
      $color, $color
    ) no-repeat right bottom;
  
  background-size: $size/2 $size/2;
}

.decor:before,
.decor:after {
  content: '';
  position: absolute;
  z-index: -1;
}

.decor:before {
  top: -$offset;
  right: 0;
  bottom: -$offset;
  left: 0;
  background: 
    radial-gradient(circle at top,
      $transparent $perc,
      $color $perc+1
    ) repeat-x top,
    radial-gradient(circle at bottom,
      $transparent $perc,
      $color $perc+1
    ) repeat-x bottom
    ;
  background-size: $size $size/2;
}

.decor:after {
  top: 0;
  right: -$offset;
  bottom: 0;
  left: -$offset;
  background: 
    radial-gradient(circle at left,
      $transparent $perc,
      $color $perc+1
    ) repeat-y left,
    radial-gradient(circle at right,
      $transparent $perc,
      $color $perc+1
    ) repeat-y right;
    ;
  background-size: $size/2 $size;
}