<button id="openModal1" class="open-modal-btn btn-color1">ボタン1をクリック</button>
<button id="openModal2" class="open-modal-btn btn-color2">ボタン2をクリック</button>
<button id="openModal3" class="open-modal-btn btn-color3">ボタン3をクリック</button>
<button id="openModal4" class="open-modal-btn btn-color4">ボタン4をクリック</button>
<button id="openModal5" class="open-modal-btn btn-color5">ボタン5をクリック</button>

<div id="myModal" class="modal">
  <div class="modal-content">
    <span id="closeModal" class="close">&times;</span>
    <p>ここにメッセージを表示します</p>
  </div>
</div>

.modal {
  display: none;
  position: fixed;
  z-index: 1;
  padding-top: 100px;
  width: 100%;
  height: 100%;
  background-color: rgba(0,0,0,0.4);
}

.modal-content {
  margin: auto;
  padding: 20px;
  border: 1px solid #888;
  width: 80%;
  background-color: #fff;
  border-radius: 20px;
  box-shadow: 0 4px 16px 0 rgba(0,0,0,0.2);
}

.close {
  color: #aaa;
  float: right;
  font-size: 28px;
  font-weight: bold;
}

.close:hover,
.close:focus {
  color: black;
  text-decoration: none;
  cursor: pointer;
}

.open-modal-btn {
  border: none;
  color: white;
  padding: 15px 32px;
  text-align: center;
  text-decoration: none;
  display: inline-block;
  font-size: 16px;
  margin: 4px 2px;
  cursor: pointer;
  border-radius: 4px;
}

.btn-color1 {
  background-color: #1d3557;
}

.btn-color2 {
  background-color: #457b9d;
}

.btn-color3 {
  background-color: #80bdc6;
}

.btn-color4 {
  background-color: #a8dadc;
}

.btn-color5 {
  background-color: #e63946;
}
window.onload = function() {
  var modal = document.getElementById('myModal');
  var btns = document.getElementsByClassName('open-modal-btn');
  var span = document.getElementsByClassName('close')[0];

  for (let i = 0; i < btns.length; i++) {
    btns[i].onclick = function() {
      modal.style.display = 'block';
    }
  }

  span.onclick = function() {
    modal.style.display = 'none';
  }

  window.onclick = function(event) {
    if (event.target == modal) {
      modal.style.display = 'none';
    }
  }
}
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