.btnStack {
  background-color: orange;
  color: #000;
  text-decoration: none;
  display: inline-block;
  padding: 6px 12px;
  margin-bottom: 0;
  font-size: 14px;
  font-weight: normal;
  line-height: 1.428571429;
  text-align: center;
  white-space: nowrap;
  vertical-align: middle;
  cursor: pointer;
  border: 1px solid transparent;
  border-radius: 4px;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  -o-user-select: none;
  user-select: none;
}
a.btnStack:hover {
  background-color: #000;
  color: #fff;
}

<script type="text/javascript" charset="utf-8">
$(document).on('ready pjax:scriptcomplete',function(){
   $('#ls-button-submit').text("LET'S START");
});
</script>

<style type="text/css">#ls-button-submit {
    border: 3px solid yellow;
    border-radius: 50%;
    background-color: red;
}
</style>