Load custom CSS (#6841)

* wip loading custom css

* read css file from profile directory and apply

* update css handler, add CLI flag to disable custom CSS, documentation

* import ExtensionAppJinjaMixin

* remove ExtensionAppJinjaMixin as a JupyterNotebookApp base class

* add type hint to ignore jinja2_env type

* fix prettier issue in docs

* add empty line; trigger new docs build

* new line caused prettier error, remove

* move custom css to different directory and update handler

* modify regex

* satisfy mypy: check for match in regex before grabbing the directory path

* load custom css in consoles page

docs/source/config_overview.md

@@ -26,6 +26,10 @@ and editing settings is similar for all the Jupyter applications.
 > - [traitlets](https://traitlets.readthedocs.io/en/latest/config.html#module-traitlets.config)
 >   provide a low-level architecture for configuration.
 
+### Disabling Custom CSS
+
+Custom CSS is loaded by default as was done with Jupyter Notebook 6. In the jupyter configuration directory, the `/.jupyter/custom/custom.css` file will be loaded unless the the application is initialized with the `custom_css` flag with the argument set to `False` as in `--JupyterNotebookApp.custom_css=False`.
+
 (configure-jupyter-server)=
 
 ## Jupyter server

notebook/app.py

@@ -1,11 +1,16 @@
 """Jupyter notebook application."""
 import os
+import re
 from os.path import join as pjoin
 
 from jupyter_client.utils import ensure_async
 from jupyter_core.application import base_aliases
+from jupyter_core.paths import jupyter_config_dir
 from jupyter_server.base.handlers import JupyterHandler
-from jupyter_server.extension.handler import ExtensionHandlerJinjaMixin, ExtensionHandlerMixin
+from jupyter_server.extension.handler import (
+    ExtensionHandlerJinjaMixin,
+    ExtensionHandlerMixin,
+)
 from jupyter_server.serverapp import flags
 from jupyter_server.utils import url_escape, url_is_absolute
 from jupyter_server.utils import url_path_join as ujoin
@@ -32,6 +37,10 @@ version = __version__
 class NotebookBaseHandler(ExtensionHandlerJinjaMixin, ExtensionHandlerMixin, JupyterHandler):
     """The base notebook API handler."""
 
+    @property
+    def custom_css(self):
+        return self.settings.get("custom_css", True)
+
     def get_page_config(self):
         """Get the page config."""
         config = LabConfig()
@@ -87,6 +96,7 @@ class NotebookBaseHandler(ExtensionHandlerJinjaMixin, ExtensionHandlerMixin, Jup
 
         page_config.setdefault("mathjaxConfig", mathjax_config)
         page_config.setdefault("fullMathjaxUrl", mathjax_url)
+        page_config.setdefault("jupyterConfigDir", jupyter_config_dir())
 
         # Put all our config in page_config
         for name in config.trait_names():
@@ -203,6 +213,27 @@ class NotebookHandler(NotebookBaseHandler):
         return self.write(tpl)
 
 
+class CustomCssHandler(NotebookBaseHandler):
+    """A custom CSS handler."""
+
+    @web.authenticated
+    def get(self):
+        """Get the custom css file."""
+
+        self.set_header("Content-Type", 'text/css')
+        page_config = self.get_page_config()
+        custom_css_file = f"{page_config['jupyterConfigDir']}/custom/custom.css"
+
+        if not os.path.isfile(custom_css_file):
+            static_path_root = re.match('^(.*?)static', page_config['staticDir'])
+            if static_path_root is not None:
+                custom_dir = static_path_root.groups()[0]
+                custom_css_file = f"{custom_dir}custom/custom.css"
+
+        with open(custom_css_file) as css_f:
+            return self.write(css_f.read())
+
+
 aliases = dict(base_aliases)
 
 
@@ -227,12 +258,25 @@ class JupyterNotebookApp(NotebookConfigShimMixin, LabServerApp):
         help="Whether to expose the global app instance to browser via window.jupyterapp",
     )
 
+    custom_css = Bool(
+        True,
+        config=True,
+        help="""Whether custom CSS is loaded on the page.
+        Defaults to True and custom CSS is loaded.
+        """,
+    )
+
     flags = flags
     flags["expose-app-in-browser"] = (
         {"JupyterNotebookApp": {"expose_app_in_browser": True}},
         "Expose the global app instance to browser via window.jupyterapp.",
     )
 
+    flags["custom-css"] = (
+        {"JupyterNotebookApp": {"custom_css": True}},
+        "Load custom CSS in template html files. Default is True",
+    )
+
     @default("static_dir")
     def _default_static_dir(self):
         return os.path.join(HERE, "static")
@@ -261,6 +305,10 @@ class JupyterNotebookApp(NotebookConfigShimMixin, LabServerApp):
     def _default_workspaces_dir(self):
         return get_workspaces_dir()
 
+    def _prepare_templates(self):
+        super(LabServerApp, self)._prepare_templates()
+        self.jinja2_env.globals.update(custom_css=self.custom_css)  # type:ignore
+
     def server_extension_is_enabled(self, extension):
         """Check if server extension is enabled."""
         try:
@@ -290,6 +338,7 @@ class JupyterNotebookApp(NotebookConfigShimMixin, LabServerApp):
         self.handlers.append(("/edit(.*)", FileHandler))
         self.handlers.append(("/consoles/(.*)", ConsoleHandler))
         self.handlers.append(("/terminals/(.*)", TerminalHandler))
+        self.handlers.append(("/custom/custom.css", CustomCssHandler))
         super().initialize_handlers()
 
     def initialize(self, argv=None):

notebook/custom/custom.css

@@ -0,0 +1,7 @@
+/*
+Placeholder for custom user CSS
+
+mainly to be overridden in profile/static/custom/custom.css
+
+This will always be an empty file
+*/

notebook/templates/consoles.html

@@ -7,6 +7,10 @@
   {% block favicon %}
   <link rel="icon" type="image/x-icon" href="{{ page_config['fullStaticUrl'] | e }}/favicons/favicon-console.ico" class="favicon">
   {% endblock %}
+
+  {% if custom_css %}
+  <link rel="stylesheet" type="text/css" href="{{ base_url | escape }}custom/custom.css">
+  {% endif %}
 </head>
 <body>
 

notebook/templates/notebooks.html

@@ -7,6 +7,10 @@
   {% block favicon %}
   <link rel="icon" type="image/x-icon" href="{{ base_url | escape }}static/favicons/favicon-notebook.ico" class="favicon">
   {% endblock %}
+
+  {% if custom_css %}
+  <link rel="stylesheet" type="text/css" href="{{ base_url | escape }}custom/custom.css">
+  {% endif %}
 </head>
 <body data-notebook="notebooks">
 

notebook/templates/terminals.html

@@ -7,6 +7,10 @@
   {% block favicon %}
   <link rel="icon" type="image/x-icon" href="{{ base_url | escape }}static/favicons/favicon-terminal.ico" class="favicon">
   {% endblock %}
+
+  {% if custom_css %}
+  <link rel="stylesheet" type="text/css" href="{{ base_url | escape }}custom/custom.css">
+  {% endif %}
 </head>
 <body>
 

notebook/templates/tree.html

@@ -7,6 +7,10 @@
   {% block favicon %}
   <link rel="icon" type="image/x-icon" href="{{ base_url | escape }}static/favicons/favicon.ico" class="favicon">
   {% endblock %}
+
+  {% if custom_css %}
+  <link rel="stylesheet" type="text/css" href="{{ base_url | escape }}custom/custom.css">
+  {% endif %}
 </head>
 <body>