Bootstrap CSS class .flex-xl-fill

    <div class="d-flex bg-secondary p-1">
        <div class="p-3 flex-xl-fill bg-primary">1</div>
        <div class="p-3 bg-info">2</div>
        <div class="p-3 bg-primary">3</div>
        <div class="p-3 bg-info">4</div>
    </div>