I'm using the jupyter notebook installed with Anaconda (I'm on Mac). Few days ago, I wanted to change the theme to have a dark background, and I followed the instructions here. Namely, I've downloaded the theme custom.css and placed it in ~/.jupyter/custom/. It worked very well.

I liked the theme, but I would like to go back to the default one (this one does not show the main toolbar, among other things). I tried to remove the custom.css from its folder, I reset my terminal, but nothing changes! I'm guessing that jupyter keeps a copy of the themes somewhere that I should delete, but I can't find it.

I have also tried uninstalling jupyter and reinstalling, following the commands:

conda update conda
conda uninstall ipython
conda install jupyter

Again, no change. I'm stuck with my black background theme with no toolbar.

My previous suggestion of deleting the custom/ directory doesn't do the trick. jupyter caches the custom.css file in other directories that are tricky to clear all together. If it doesn't find a folder custom with .css file inside it it looks in other locations to pick up a .css file. Also, I'm not sure if every location is actually deleted when you uninstall jupyter.

The easiest solution is to delete the old custom.css and replace it with a new empty custom.css file. jupyter picks that up and goes back to its default look.