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

<style>
    viewer {
        position: relative;
        overflow: hidden;
        /* Start stage */
        flex: 1;
        z-index: 1;
        justify-content: center;
        align-items: center;

        width: 100%;
        height: 100%;
    }

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

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

<nav-bar></nav-bar>