There is extra space between .domino elements why, how can I get rid of it?
.domino{
  letter-spacing: 0px;
  display: inline-block;
  background-color: #e0d0b0;
  height: 150px;
  width: 100px;
  border-radius: 10px;
  text-align: center;
  font-size: 400%;
  font-family:Arial Black;
  position: relative;
  color: rgba(230,0,0, 0.9);
  text-shadow: 
    -1px 1px rgba(255,255,255,0.75),
    1px -1px rgba(0,0,0,0.5),
    2px -2px rgba(0,0,0,0.5),
    3px -3px rgba(0,0,0,0.5);
}
.domino .heart{
  content: "❤";
  position: absolute;
  top: 50%;
  left: 0px;
  width: 100%;
  font-size: 60%;
}
.heart:after{
  position: absolute;
  content: "";
  height: 50px;
  width: 50px;
  border-radius: 50px;
  left: 27px;
  background: 
  -webkit-box-shadow: inset 2px -2px 2px 0px rgba(255,255,255,0.75), inset -2px 2px 2px 0px rgba(0,0,0,0.5);
  -moz-box-shadow: inset 2px -2px 2px 0px rgba(255,255,255,0.75), inset -2px 2px 2px 0px rgba(0,0,0,0.5);
  box-shadow: inset 2px -2px 2px 0px rgba(255,255,255,0.75), inset -2px 2px 2px 0px rgba(0,0,0,0.5);
}
.heart:before{
  position: absolute;
  content: "";
  box-shadow: -1px 1px 1px 0px rgba(255,255,255,0.6), inset -2px 2px 1px 0px rgba(0,0,0,0.75);
  left: 45px;
  top: 23px;
  height: 10px;
  width: 10px;
  border-radius: 10px;
}
#rack{
  margin: 25% 10%
}
.wood {
  border-radius: 5px;
  position: relative;
  background-image: radial-gradient(#EFBF7F,#955724);
  -webkit-background-size: 100%;
  padding: 20px 20px 35px 35px;
  z-index: 0;
  max-width: 460px;
  box-shadow:
    -2px 4px rgb(100,50,25),
    -4px 6px rgb(100,50,25),
    -6px 8px rgb(100,50,25),
    -8px 10px rgb(100,50,25),
    -10px 12px rgb(100,50,25),
    -45px 25px 5px rgba(0,0,0,0.5);
}
/* Background from http://lea.verou.me/css3patterns/#upholstery */
body{
  background:
  radial-gradient(hsl(0, 100%, 27%) 4%, hsl(0, 100%, 18%) 9%, hsla(0, 100%, 20%, 0) 9%) 0 0,
  radial-gradient(hsl(0, 100%, 27%) 4%, hsl(0, 100%, 18%) 8%, hsla(0, 100%, 20%, 0) 10%) 50px 50px,
  radial-gradient(hsla(0, 100%, 30%, 0.8) 20%, hsla(0, 100%, 20%, 0)) 50px 0,
  radial-gradient(hsla(0, 100%, 30%, 0.8) 20%, hsla(0, 100%, 20%, 0)) 0 50px,
  radial-gradient(hsla(0, 100%, 20%, 1) 35%, hsla(0, 100%, 20%, 0) 60%) 50px 0,
  radial-gradient(hsla(0, 100%, 20%, 1) 35%, hsla(0, 100%, 20%, 0) 60%) 100px 50px,
  radial-gradient(hsla(0, 100%, 15%, 0.7), hsla(0, 100%, 20%, 0)) 0 0,
  radial-gradient(hsla(0, 100%, 15%, 0.7), hsla(0, 100%, 20%, 0)) 50px 50px,
  linear-gradient(45deg, hsla(0, 100%, 20%, 0) 49%, hsla(0, 100%, 0%, 1) 50%, hsla(0, 100%, 20%, 0) 70%) 0 0,
  linear-gradient(-45deg, hsla(0, 100%, 20%, 0) 49%, hsla(0, 100%, 0%, 1) 50%, hsla(0, 100%, 20%, 0) 70%) 0 0;
  background-color: #300; 
  background-size: 100px 100px;
}
.green{
  color: rgba(0,180,100, 0.9);
}
.orange{
  color: rgba(255,150,0, 0.9);
}
.black{
  color: rgba(0,0,0, 0.75);
}
<div id="rack">
  <div class="wood">
    <span class="domino green">
      <span class="num">4</span>
      <span class="heart">❤</span>
    </span>
    <span class="domino orange">
      <span class="num">2</span>
      <span class="heart">❤</span>
    </span>
     <span class="domino">
      <span class="num">0</span>
      <span class="heart">❤</span>
    </span>
    <span class="domino black">
      <span class="num">6</span>
      <span class="heart">❤</span>
    </span>
    <span class="domino">
      <span class="num">9</span>
      <span class="heart">❤</span>
    </span>
  </div>
</div>