<div class="uk-section uk-padding-remove uk-height-viewport">

    <style>
        .test-background-2 { background-image: repeating-linear-gradient(-45deg, rgba(200,200,200,0.4), rgba(200,200,200,0.4) 25px, rgba(50,50,50,0.15) 25px, rgba(50,50,50,0.15) 50px); }
    </style>

    <div class="uk-container uk-container-expand uk-background-muted uk-height-viewport uk-flex uk-flex-middle">
        <div class="uk-panel uk-margin-medium-top uk-margin-medium-bottom test-background uk-flex-auto">
            <h2 class="uk-h5 uk-padding">Expand</h2>

            <div class="uk-container test-background-1 uk-margin-medium-top uk-margin-medium-bottom">
                <div class="uk-panel uk-margin-medium-top uk-margin-medium-bottom test-background">
                    <h2 class="uk-h5 uk-padding">Default</h2>

                    <div class="uk-container uk-container-small test-background-2 uk-margin-medium-bottom">
                        <div class="uk-panel uk-margin-medium-top uk-margin-medium-bottom test-background">
                            <h2 class="uk-h5 uk-padding">Small</h2>
                        </div>
                    </div>

                </div>
            </div>

        </div>
    </div>

</div>