<!DOCTYPE html>
<html lang="ja">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<style>a {
  display: inline-block;
  text-decoration: none;
  color: #FFF;
  font-weight: bold;
  text-align: center;
  margin: 10px;
  width: 100px;
  padding: 0.5em 2em;
}
span{
  color: #FF3399;
}
.btn{
  position: relative;
  border-top: solid 3px #142c5b;
  border-bottom: solid 3px #142c5b;
  color: #142c5b;
}

.btn:before, .btn:after {
  content: '';
  position: absolute;
  top: -7px;
  width: 3px;
  height: calc(100% + 14px);
  background-color: #142c5b;
  transition: .3s;
}
.btn:before {
  left: 7px;
}
.btn:after {
  right: 7px;
}</style>
</head>
<body>
<a class="btn" href="#">お し て <span>&#9829;</span>
</a>
<script>
</script>
</body>
</html>
a {
  display: inline-block;
  text-decoration: none;
  color: #FFF;
  font-weight: bold;
  text-align: center;
  margin: 10px;
  width: 100px;
  padding: 0.5em 2em;
}
span{
  color: #FF3399;
}
.btn{
  position: relative;
  border-top: solid 3px #142c5b;
  border-bottom: solid 3px #142c5b;
  color: #142c5b;
}

.btn:before, .btn:after {
  content: '';
  position: absolute;
  top: -7px;
  width: 3px;
  height: calc(100% + 14px);
  background-color: #142c5b;
  transition: .3s;
}
.btn:before {
  left: 7px;
}
.btn:after {
  right: 7px;
}