Vycentrování Action buttonu

.button_col {
  float: left;
  clear: both;
  background: #690 url(images/bg_left.png) no-repeat;
  padding: 0 0 0 10px;
  margin: 5px 0;
margin-left: auto;
margin-right: auto;
}

.button_col a{
  float: left;
  
width: 230px;
height: 40px;
  background: url(images/bg_stretch.png) repeat-x left top;
  line-height: 40px;
  padding: 0 1px;
  color: #fff;
  font-size: 1.3em;
  text-decoration: none;
  border-bottom: none;
}
.button_col span {
  background: url(images/bg_right.png) no-repeat;
  float: left;
  width: 10px;
  height: 40px;
margin-left: auto;
margin-right: auto;
}
.clear {
  clear: both;
}