<!DOCTYPE html>
<meta charset="utf-8">
<title>Spaced Gradient</title>
<style>
    #foo {
        width: calc(4 * 30px + 3 * 5px);
        height: calc(4 * 30px + 3 * 5px);
        background: radial-gradient(transparent 50%, #36c 50%);
        background-size: 30px 30px;
        background-repeat: space;
    }
</style>
<body>
    <div id="foo"></div>
</body>