.btn-flat-vertical-border {
  position: relative;
  display: inline-block;
  font-weight: bold;
  padding: 0.5em 1em;
  text-decoration: none;
  border-left: solid 4px #006400;
  border-right: solid 4px #006400;
  color: #000000;
  background: #98fb98;
  transition: .4s;
}

.btn-flat-vertical-border:hover {
  background: #ffffe0;
  color: #ff0000;
}