.out-of-stock {
   visibility:hidden;
}
.out-of-stock:before {
   visibility:visible;
   content:"Sold"; /* use desired label */
   display: inline-block;
   border-bottom: 2px solid;
}

.out-of-stock-button-inner {
   visibility:hidden;
}
.out-of-stock-button-inner:before {
   visibility:visible;
   content:""; /* use desired label */
   display: block;
}

.in-stock {
   visibility:hidden;
}
.in-stock:before {
   visibility:visible;
   content:"Available"; /* use desired label */
   display: inline-block;
   border-bottom: 2px solid;
}

.in-stock-button-inner {
   visibility:hidden;
}
.in-stock-button-inner:before {
   visibility:visible;
   content:"Available"; /* use desired label */
   display: block;
}

.out-of-stock-button-inner {
    position: relative !important;
    top: 9px !important; /* you can adjust this value */
}