如何让点击触发的Modal弹窗固定位置不随滚动移动？

你的弹窗会跟着页面滚动移动，核心问题是.modal容器没有占满整个视口，且定位后的尺寸设置不符合需求，导致弹窗内容的固定定位没有正确参照视口。以下是具体修改方案：

关键CSS修改 #

1. 调整.modal容器样式 #

将.modal改为铺满整个视口，同时保留页面滚动能力：

.modal {
  display: none; 
  position: fixed; 
  z-index: 1; 
  left: 0;
  top: 0;
  width: 100%; /* 占满视口宽度 */
  height: 100%; /* 占满视口高度 */
  overflow: visible; /* 允许页面滚动 */
  background-color: rgba(0,0,0,0.5); /* 可选：添加半透明背景，增强视觉区分 */
}

2. 确认弹窗内容的固定定位 #

保留.modal-content的position: fixed，确保它始终固定在视口中央：

.modal-content {
  width: 70%;
  height: 80%;
  position: fixed;
  left: 0;
  right: 0;
  top: 0;
  bottom: 0;
  margin: auto;
  max-width: 100%;
  max-height: 100%;
  background-color: #0E0E0E;
  border: 2px solid #FFFFFF;
}

修改后的完整代码 #

<html>
  <head>
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
  

<style>

  /* The Modal (background) */
.modal {
  display: none; 
  position: fixed; 
  z-index: 1; 
  left: 0;
  top: 0;
  width: 100%; 
  height: 100%; 
  overflow: visible;
  background-color: rgba(0,0,0,0.5);
}

/* Modal Content/Box */
.modal-content {
   width: 70%;
        height: 80%;
        position: fixed;
        left: 0;
        right: 0;
        top: 0;
        bottom: 0;
        margin: auto;
        max-width: 100%;
        max-height: 100%;
  background-color: #0E0E0E;
  
  
  border: 2px solid #FFFFFF;
 
  
}

/* The Close Button */
.close {
  color: #aaa;
  float: right;
  font-size: 28px;
  font-weight: bold;
  position: relative;
  left: -10px;
  top: -1px;
}

.close:hover,
.close:focus {
  color: black;
  text-decoration: none;
  cursor: pointer;
}
@media only screen and (min-width: 600px) {
  .col-s-1 {width: 8.33%;}
  .col-s-2 {width: 16.66%;}
  .col-s-3 {width: 25%;}
  .col-s-4 {width: 33.33%;}
  .col-s-5 {width: 41.66%;}
  .col-s-6 {width: 50%;}
  .col-s-7 {width: 58.33%;}
  .col-s-8 {width: 66.66%;}
  .col-s-9 {width: 75%;}
  .col-s-10 {width: 83.33%;}
  .col-s-11 {width: 91.66%;}
  .col-s-12 {width: 100%;}
}

@media only screen and (min-width: 768px) {
  .col-1 {width: 8.33%;}
  .col-2 {width: 16.66%;}
  .col-3 {width: 25%;}
  .col-4 {width: 33.33%;}
  .col-5 {width: 41.66%;}
  .col-6 {width: 50%;}
  .col-7 {width: 58.33%;}
  .col-8 {width: 66.66%;}
  .col-9 {width: 75%;}
  .col-10 {width: 83.33%;}
  .col-11 {width: 91.66%;}
  .col-12 {width: 100%;}
}
.video{
           width: 65%;
        height: 65%;
        position: absolute;
        left: 0;
        right: 0;
        top: 0;
        bottom: 0;
        margin: auto;
        max-width: 100%;
        max-height: 100%;
 
}
.myBtn{
  margin-top: 20%;

}
</style>
</head>
        <body>   
<!-- The Modal -->
<div id="myModal" class="modal">

  <!-- Modal content -->
  <div class="modal-content">
    <span class="close">&times;</span>
    <center>
    <div class="video">
        
    <video src="https://cdn.shopify.com/videos/c/o/v/1ef399dd4bb345e485f6e4784a9d0031.mp4" type="video/mp4" autoplay width="100%" height="100%"></video>
</center>
    </div>
    
  </div>
  <button class="myBtn" id="myBtn">Open Modal</button>
   
 

          </body> 
            <script>
              // Get the modal
var modal = document.getElementById("myModal");

var btn = document.getElementById("myBtn");

var span = document.getElementsByClassName("close")[0];

btn.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";
  }
}
            </script>


  </html>

修改后效果：弹窗会固定在视口中央，页面可以正常滚动，点击弹窗外部区域即可关闭弹窗。

内容的提问来源于stack exchange，提问作者Mellemo