<!DOCTYPE html>
<html>
<head>
<style type="text/css">
#parent {
width: 200px;
}
#block1 {
height: 40px;
margin-bottom: 10%;
background-color: green;
}
#block2 {
height: 40px;
margin-top: 25%;
background-color: green;
}
</style>
</head>
<body>
<div id="parent">
<div id="block1"></div>
<div id="block2"></div>
</div>
</body>
</html>