Overlaying <span> doesn't work in IE6

<li>
  <span>overlay</span>
  content
</li>


li {
   position: relative;
   height:65px;
   overflow: hidden;
}
li span {
    background: url(../img/bullet_grey.png) no-repeat;
    width: 20px;
    height: 20px;
    positi开发者_JAVA百科on: absolute;
    top: 50px;
    left: 10px;
}

This works in all browsers except IE6, which just hides the SPAN somewhere. How do I fix it?

Thanks!

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This here should guide you to the solution.