<!DOCTYPE html>
<html>
<head>
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<style>
div {
    width: 100%;
    height: 400px;
    background-image: url('img_flowers.jpg');
    background-size: 100% 100%;
    border: 1px solid red;
}
</style>
</head>
<body>

<p>Resize the browser window to see the effect.</p>

<div></div>

</body>
</html>

Resize the browser window to see the effect.