button {
  position:relative;
  display:block;
  margin-left:auto;
  margin-right:auto;
  padding-left:14px;
  padding-right:14px;
  box-sizing:border-box;
  font-size:18px;
  text-align:center;
  text-decoration:none;
  line-height:2.55555556;
  border-radius:5px;
  -webkit-tap-highlight-color:transparent;
  overflow:hidden;
  color:#000000;
  background-color:#F8F8F8;
}

button{
    border:none;
}
或者
button{
    outline: none;
}

button::after {
  border: none;
}