padding-bottom

значения свойства:

0
size
%
inherit

css/style.css

* {
margin: 0;
padding: 0;
}
.a, #p1, .b {
width: 300px;
height: 50px;
margin: 30px 0 30px 30px;
background-color: #7092BE;
}
.a {
padding-bottom: 5px;
}

* {
 margin: 0;
 padding: 0;
}

.a, #p1, .b {
 width: 300px;
 height: 50px;
 margin: 30px 0 30px 30px;
 background-color: #7092BE;
}

.a {
 padding-bottom: 5px;
}

index.html

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>New Page</title>
<link href="css/style.css" rel="stylesheet" />
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
</head>
<body>
<p class="a">To be or not to be?</p>
<p id="p1">To be or not to be?</p>
<p class="b">To be or not to be?</p>
<script>
/*JavaScript*/
document.getElementById("p1").style.paddingBottom = "20px";
/*jQuery*/
$(document).ready(function () {
$(".b").css({ "padding-bottom": "50px" });
});
</script>
</body>
</html>

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>New Page</title>
<link href="css/style.css" rel="stylesheet" />
<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
</head>
<body>
<p class="a">To be or not to be?</p>
<p id="p1">To be or not to be?</p>
<p class="b">To be or not to be?</p>
<script>
/*JavaScript*/
document.getElementById("p1").style.paddingBottom = "20px";
/*jQuery*/
$(document).ready(function () {
$(".b").css({ "padding-bottom": "50px" });
});
</script>
</body>
</html>