Neon Outline Button

<button class="neon-btn">Subscribe</button>

.neon-btn {
  padding: 12px 28px;
  background: transparent;
  border: 1px solid #22d3ee;
  border-radius: 8px;
  color: #22d3ee;
  font: 500 13px/1 system-ui, sans-serif;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  cursor: pointer;
  transition: box-shadow .3s ease, color .3s ease, background .3s ease;
}
.neon-btn:hover {
  color: #fff;
  background: rgba(34, 211, 238, 0.08);
  box-shadow: 0 0 0 1px #22d3ee, 0 0 20px rgba(34, 211, 238, 0.5);
}