Add the custom CSS handler is self.custom_css is set

[jtpio]

Investigate some ideas discussed in #7175

[github-actions]

👈 Launch a Binder on branch jtpio/notebook/custom-css

[jtpio]

Starting notebook with jupyter notebook --custom-css still seems to work with Notebook.

Testing with:

/* Modify Jupyter Styles */
#top-panel-wrapper,
#jp-top-bar {
  background-color: #aecad4 !important;
}

#menu-panel-wrapper,
#jp-MainMenu,
#menu-panel {
  background-color: #aecad4 !important;
}

.jp-NotebookPanel-toolbar {
  background-color: #aecad4 !important;
}
.lm-MenuBar-content {
  color: #02484d;
}

However it seems to be preventing lab to pick up the custom css (the top bar should be styled):

[jtpio]

Although setting the lab trait explicitly seems to be doing the trick: jupyter notebook --custom-css --LabApp.custom_css=True: