diff --git a/dargs/notebook.py b/dargs/notebook.py
index 30b9708..b69b31b 100644
--- a/dargs/notebook.py
+++ b/dargs/notebook.py
@@ -298,7 +298,11 @@ def print_html(self, _level=0, _last_one=True):
         else:
             buff.append(r"""<code class="dargs-code">""")
             buff.append(
-                json.dumps(self.data, indent=2).replace("\n", f"{linebreak}{indent}")
+                json.dumps(self.data, indent=2)
+                .replace(" ", "&nbsp;")
+                .replace(
+                    "\n", f"""</code>{linebreak}{indent}<code class="dargs-code">"""
+                )
             )
             if not _last_one:
                 buff.append(",")
diff --git a/dargs/sphinx.py b/dargs/sphinx.py
index 5fe46e2..4e61770 100644
--- a/dargs/sphinx.py
+++ b/dargs/sphinx.py
@@ -171,6 +171,7 @@ def _test_argument() -> Argument:
         doc=doc_test,
         sub_fields=[
             Argument("test_argument", dtype=str, doc=doc_test, default="test"),
+            Argument("test_list", dtype=List[int], optional=True),
         ],
         sub_variants=[
             Variant(
diff --git a/docs/nb.ipynb b/docs/nb.ipynb
index 1793515..4b3d844 100644
--- a/docs/nb.ipynb
+++ b/docs/nb.ipynb
@@ -21,6 +21,11 @@
     "jstr = \"\"\"\n",
     "{\n",
     "    \"test_argument\": \"test1\",\n",
+    "    \"test_list\": [\n",
+    "        1,\n",
+    "        2,\n",
+    "        3\n",
+    "    ],\n",
     "    \"test_variant\": \"test_variant_argument\",\n",
     "    \"test_repeat\": [\n",
     "        {\"test_repeat_item\": false},\n",