Fix vtk_slicer (#4722)

* fix vtk_slicer

* reset width

---------

Co-authored-by: Marc Skov Madsen <masma@orsted.dk>

examples/gallery/vtk_slicer.ipynb

@@ -25,7 +25,7 @@
     "css_files = ['https://golden-layout.com/files/latest/css/goldenlayout-base.css',\n",
     "             'https://golden-layout.com/files/latest/css/goldenlayout-dark-theme.css']\n",
     "\n",
-    "pn.extension('vtk', js_files=js_files, css_files=css_files, theme='dark')\n",
+    "pn.extension('vtk', js_files=js_files, css_files=css_files, theme='dark', sizing_mode=\"stretch_width\")\n",
     "\n",
     "hv.renderer('bokeh').theme = 'dark_minimal'\n",
     "hv.opts.defaults(hv.opts.Image(responsive=True, tools=['hover']))"
@@ -109,7 +109,11 @@
     "    colormap='Rainbow Desaturated'\n",
     ")\n",
     "\n",
-    "dataset_selection.link(target=volume, value='object')\n",
+    "@pn.depends(dataset_selection, watch=True)\n",
+    "def update_volume_object(value):\n",
+    "    controller.loading=True\n",
+    "    volume.object = value\n",
+    "    controller.loading=False\n",
     "\n",
     "volume_controls = volume.controls(jslink=False, parameters=[\n",
     "    'render_background', 'display_volume', 'display_slices',\n",
@@ -147,10 +151,11 @@
     "dmap_j = rasterize(hv.DynamicMap(image_slice_j))\n",
     "dmap_k = rasterize(hv.DynamicMap(image_slice_k))\n",
     "\n",
-    "controller = pn.WidgetBox(\n",
+    "controller = pn.Column(\n",
     "    pn.Column(dataset_selection, toggle_parallel_proj, *volume_controls[1:]),\n",
     "    pn.Param(smoother, parameters=['smooth_level', 'order']),\n",
-    "    pn.layout.VSpacer()\n",
+    "    pn.panel(\"This app demos **advanced 3D visualisation** using [Panel](https://panel.holoviz.org/) and [PyVista](https://docs.pyvista.org/).\", margin=(5,15)),\n",
+    "    pn.layout.VSpacer(),\n",
     ")"
    ]
   },
@@ -176,6 +181,11 @@
     "    {%% set slicer_id = get_id() %%}\n",
     "    <div id='{{slicer_id}}'></div>\n",
     "{%% endif %%}\n",
+    "<style>\n",
+    ":host {\n",
+    "    width: auto;\n",
+    "}\n",
+    "</style>\n",
     "\n",
     "<script>\n",
     "var config = {\n",