<div class="btn-box">
  <button>CLICK ME</button>
</div>

* {
  margin: 0;
  padding: 0;
}
.btn-box {
  width: 100%;
  display: flex;
  justify-content: center;
}
button {
  margin: 2em;
  font-size: 2em;
  background-color: #ff9f00;
  border: none;
  padding: 1em;
  border-radius: 0.5em;
  font-weight: 600;
  cursor: pointer;
}
button:hover {
  background-color: #c02907;
}