<style>
    * {
        border: 1px solid black;
        grid-template-columns: 1fr 1fr;
    }

    .grid-container {
        display: grid;
    }

    .a {
        grid-column: 1 / span 3;
        grid-row: 1;
    }
</style><div class="grid-container"><div class="a">1</div><div>2</div></div>