Babylon.js/Viewer/assets/templates/default/defaultViewer.html

<style>
    .babylonjs-canvas {
        flex: 1;
        width: 100%;
        height: 100%;
        touch-action: none;
    }

    nav-bar {
        position: absolute;
        height: 160px;
        width: 100%;
        bottom: 0;
        opacity: 0.3;
        background-color: black;
        color: white;
        transition: 1s;

        align-items: center;
        justify-content: center;
        display: flex;

        flex-direction: column;
    }

    /* Big screens have room for the entire navbar */

    @media screen and (min-width: 768px) {
        nav-bar {
            flex-direction: row;
            justify-content: space-between;
            height: 80px;
        }
    }
</style>

<canvas class="babylonjs-canvas" id="{{canvasId}}">
</canvas>

<nav-bar></nav-bar>