style.css

.btn{
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  background: pink;
  font-size: 20px;
  color: white;
  padding: 10px 30px;
  cursor: pointer;
}


.modal {
  position: fixed;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  background-color: rgba(0, 0, 0, 0.3);
  opacity: 0;
  visibility: hidden;
}
.modal-box {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  background-color: pink;
  padding: 1rem 1.5rem;
  width: 24rem;
  border-radius: 0.5rem;
}
.close-button {
  float: right;
  width: 1.5rem;
  line-height: 1.5rem;
  text-align: center;
  cursor: pointer;
  border-radius: 0.25rem;
  background-color: lightgray;
}

.show-modal {
  opacity: 1;
  visibility: visible;
  transform: scale(1.0);
}