Essays and records to facilitate their access to fellow travelers, it is best to learn HTML learning CSS.
#------------------------------------------------I ------------------------------------------- dividing line is a shame
Three colors, green, black and white using the z-index to show the level of control
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<div style="z-index:10; position: fixed;top: 50%;left:50%;
margin-left: -250px;margin-top: -200px; background-color:white;height: 400px;width:500px; ">
<input type="text" />
<input type="text" />
<input type="text" />
</div>
<div style="z-index:9; position: fixed;background-color: black;
top:0;
bottom: 0;
right: 0;
left: 0;
opacity: 0.5;
"></div>
<div style="height: 5000px;background-color: green;">
asdfasdf
</div>
</body>
</html>
effect:
z-index of the large number of the above, the above code 10 in the outermost layer and then 9