如图所示：fixed Modal最后的实现效果。大小可随着页面进行缩放，当高度不足时，会出现垂直滚动条。
代码如下：
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Modal</title>
<link rel="stylesheet" href="https://cdn.bootcss.com/font-awesome/4.7.0/css/font-awesome.min.css" />
</head>
<style>
@import 'https://fonts.googleapis.com/css?family=Prompt:400,700';
.modal {
/* This way it could be display flex or grid or whatever also. */
display: block;
/* Probably need media queries here */
width: 600px;
max-width: 100%;
height: 400px;
max-height: 100%;
position: fixed;
z-index: 100;
left: 50%;
top: 50%;
/* Use this for centering if unknown width/height */
transform: translate(-50%, -50%);
/* If known, negative margins are probably better (less chance of blurry text). */
/* margin: -200px 0 0 -200px; */
background: white;
/*box-shadow: 0 0 60px 10px rgba(0, 0, 0, 0.9);*/
}
.closed {
display: none;
}
.modal-overlay {
position: fixed;
top: 0;
left: 0;
width: 100%;
height: 100%;
z-index: 50;
background: rgba(0, 0, 0, 0.5);
}
.modal-guts {
position: absolute;
top: 0;
left: 0;
width: 100%;
height: 100%;
overflow: auto;
padding: 20px 50px 20px 20px;
}
* {
box-sizing: border-box;
margin: 0;
padding: 0;
}
body {
/*background-color: #556;*/
/*background-image: linear-gradient(30deg, #445 12%, transparent 12.5%, transparent 87%, #445 87.5%, #445), linear-gradient(150deg, #445 12%, transparent 12.5%, transparent 87%, #445 87.5%, #445), linear-gradient(30deg, #445 12%, transparent 12.5%, transparent 87%, #445 87.5%, #445), linear-gradient(150deg, #445 12%, transparent 12.5%, transparent 87%, #445 87.5%, #445), linear-gradient(60deg, #99a 25%, transparent 25.5%, transparent 75%, #99a 75%, #99a), linear-gradient(60deg, #99a 25%, transparent 25.5%, transparent 75%, #99a 75%, #99a);*/
background-size: 80px 140px;
background-position: 0 0, 0 0, 40px 70px, 40px 70px, 0 0, 40px 70px;
font-family: 'Prompt', sans-serif;
}
ul {
margin: 10px 0 10px 30px;
}
li,
p {
margin: 0 0 10px 0;
}
h1 {
margin: 0 0 20px 0;
}
.modal .close-button {
position: absolute;
/* don't need to go crazy with z-index here, just sits over .modal-guts */
z-index: 1;
top: 10px;
/* needs to look OK with or without scrollbar */
right: 20px;
border: 0;
background: black;
color: white;
padding: 5px 10px;
font-size: 1.3rem;
}
.open-button {
border: 0;
position: absolute;
top: 50%;
left: 50%;
transform: translate(-50%, -50%);
background: lightgreen;
color: white;
padding: 10px 20px;
border-radius: 10px;
font-size: 21px;
}
</style>
<body>
<div class="modal-overlay" id="modal-overlay"></div>
<div class="modal fade" id="modal">
<button class="close-button" id="close-button"><i class="fa fa-remove"></i></button>
<div class="modal-guts">
<h1>Modal Example</h1>
<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Repudiandae expedita corrupti laudantium aperiam, doloremque explicabo ipsum earum dicta saepe delectus totam vitae ipsam doloribus et obcaecati facilis eius assumenda, cumque.</p>
<p>Lorem ipsum dolor sit amet, consectetur adipisicing elit. Repudiandae expedita corrupti laudantium aperiam, doloremque explicabo ipsum earum dicta saepe delectus totam vitae ipsam doloribus et obcaecati facilis eius assumenda, cumque.</p>
</div>
</div>
<button id="open-button" class="open-button">Open Button</button>
<script type="text/javascript">
var modal = document.querySelector("#modal");
var modalOverlay = document.querySelector("#modal-overlay");
var closeButton = document.querySelector("#close-button");
var openButton = document.querySelector("#open-button");
closeButton.addEventListener("click", function() {
modal.classList.toggle("closed");
modalOverlay.classList.toggle("closed");
});
openButton.addEventListener("click", function() {
modal.classList.toggle("closed");
modalOverlay.classList.toggle("closed");
});
</script>
</body>
</html>
