creating overlay in css code example
Example 1: css overlay
#hero{
background-image:url();
background-size:cover;
background-position:top center;
position:relative;
}
#hero::after{
content:'';
position:absolute;
left:0;
top:0;
height:100%;
width:100%;
background-color:black;
opacity:0.7;
}
Example 2: overlay a box in css
<html>
<body>
<div class="overlay"></div>
<body>
<html>