Generated by SassMeister.com.

SassMeister-input-HTML.html

<ul>
  <li><span>Box1</span></li>
   <li><span>Box1</span></li>
   <li><span>Box1</span></li>
   <li><span>Box1</span></li>
   <li><span>Box1</span></li>
</ul>

SassMeister-input.scss

// ----
// Sass (v3.3.0.rc.5)
// Compass (v1.0.0.alpha.18)
// ----

li{
  position:relative;
  width:100px;
  height:100px;
  list-style:none;
  background:black;
  margin:20px;
  text-indent:-9999px;
  & > span {
  position:absolute;
  background:blue;
  width:20px;
  height:20px;
  top:0;
  right:0;
  left:0;
  bottom:0;
  margin:auto;
  }
}

SassMeister-output.css

li {
  position: relative;
  width: 100px;
  height: 100px;
  list-style: none;
  background: black;
  margin: 20px;
  text-indent: -9999px;
}
li > span {
  position: absolute;
  background: blue;
  width: 20px;
  height: 20px;
  top: 0;
  right: 0;
  left: 0;
  bottom: 0;
  margin: auto;
}

SassMeister-rendered.html

<ul>
  <li><span>Box1</span></li>
   <li><span>Box1</span></li>
   <li><span>Box1</span></li>
   <li><span>Box1</span></li>
   <li><span>Box1</span></li>
</ul>