Добавьте очень тонкую тень (CSS) в элемент (HTML)
/*CSS/STYLE.CSS START*/
p {
padding: 10px;
}
.box {
padding: 20px;
width: 50%;
margin: 30px auto;
background: #666;
color: #fff;
}
/* offset-x | offset-y | blur-radius | spread-radius | color */
#box1 {
box-shadow: 0px 2px 7px 1px grey;
}
/*CSS/STYLE.CSS STOP*/
----------------------------------------------------------------------------
/*HTML START*/
<!doctype html>
<html>
<head>
<meta charset="utf-8">
<meta name="description" content="">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>Untitled</title>
<link rel="stylesheet" href="css/style.css">
</head>
<body>
<div id="box1" class="box">Box1</div>
<div id="box2" class="box">Box2</div>
<div id="box3" class="box">Box3</div>
</body>
</html>
/*HTML STOP*/
Zaphod Beeblebrox