Add notebook test for CSS loader

tests_notebooks/static/styles/test.css

@@ -0,0 +1,3 @@
+.red-text {
+  color: rgb(255, 0, 0);
+}

tests_notebooks/test_notebook.ipynb

@@ -0,0 +1,67 @@
+{
+  "cells": [
+    {
+      "cell_type": "code",
+      "execution_count": null,
+      "metadata": {},
+      "outputs": [],
+      "source": [
+        "import ipywidgets as ipw"
+      ]
+    },
+    {
+      "cell_type": "code",
+      "execution_count": null,
+      "metadata": {},
+      "outputs": [],
+      "source": [
+        "from aiida import load_profile\n",
+        "\n",
+        "load_profile();"
+      ]
+    },
+    {
+      "cell_type": "code",
+      "execution_count": null,
+      "metadata": {},
+      "outputs": [],
+      "source": [
+        "from aiidalab_widgets_base.utils.loaders import load_css\n",
+        "\n",
+        "load_css(css_path=\"static/styles/test.css\")"
+      ]
+    },
+    {
+      "cell_type": "code",
+      "execution_count": null,
+      "metadata": {},
+      "outputs": [],
+      "source": [
+        "label = ipw.Label(\"Testing\")\n",
+        "label.add_class(\"red-text\")\n",
+        "display(label)"
+      ]
+    }
+  ],
+  "metadata": {
+    "kernelspec": {
+      "display_name": "Python 3 (ipykernel)",
+      "language": "python",
+      "name": "python3"
+    },
+    "language_info": {
+      "codemirror_mode": {
+        "name": "ipython",
+        "version": 3
+      },
+      "file_extension": ".py",
+      "mimetype": "text/x-python",
+      "name": "python",
+      "nbconvert_exporter": "python",
+      "pygments_lexer": "ipython3",
+      "version": "3.9.13"
+    }
+  },
+  "nbformat": 4,
+  "nbformat_minor": 2
+}

tests_notebooks/test_notebooks.py

@@ -5,6 +5,15 @@
 from selenium.webdriver.common.keys import Keys
 
 
+def test_loaded_css(selenium_driver):
+    driver = selenium_driver("tests_notebooks/test_notebook.ipynb")
+    element = driver.find_element(By.CLASS_NAME, "red-text")
+    assert element.value_of_css_property("color") in (
+        "rgba(255, 0, 0, 1)",  # Chrome
+        "rgb(255, 0, 0)",  # Firefox
+    )
+
+
 def test_notebook_service_available(notebook_service):
     url, token = notebook_service
     response = requests.get(f"{url}/?token={token}")