<style>
    .checkboard {
        background-image:
            linear-gradient(45deg, black 25%, transparent 25%, transparent 75%, black 75%, black),
            linear-gradient(45deg, black 25%, transparent 25%, transparent 75%, black 75%, black);
        background-position: 0 0, 50px 50px;
        background-size: 25% 25%;
        outline: 2px solid red;
        height: 400px;
        width: 400px;

    }
</style>
<body>
    <div class="checkboard"></div>
</body>
