span.tool {
  text-decoration: none;
  position: relative;   /* this is key */
  cursor: default;
}
 
span.tool span.tip {
  text-decoration: none;
  display: none;        /* so is this */
}

/* tooltip will display on :hover event */
 
span.tool:hover span.tip {
  text-decoration: none;
  width: 100px;
  display: block;
  z-index: 100;
  position: absolute;
  top: 1.6em;
  left: 0;
  padding: 10px;
  border: 1px solid #336;
  background-color: #f7f7ee;
  font: 0.9em/1.2em arial, helvetica, sans-serif;
  text-align: left;
  color: #000;
}

#content span.tool::after {
  text-decoration: none;
  padding-left: 2px;            /* eye candy */
  content: url(/img/bubble.gif);
}