Custom CSS in Jupyter (Lab) Notebook

Hi,

I’m trying to apply custom CSS to bokeh widgets displayed in a jupyter(lab) notebook. Motivation: Since bokeh ~3.4ish, widget font colors have not played nice with the jupyterlab dark theme - text often renders white on white background.

I’ve added a custom.css in the ~/.jupyter/config/custom directory:

bokeh_widget {
    font-weight: bold;
    color: black;
}

Example ipynb with Widget:

import pandas as pd

from bokeh.layouts import row 
from bokeh.models.widgets import Select
from bokeh.io import show, output_notebook

output_notebook()

months = list(pd.date_range(start='2024-01-01', periods=12, 
                                            freq='ME').strftime('%b'))

sel_month = Select(title='Select Month:', value='All', 
                      options=['All']+months, css_classes=['bokeh_widget'])


def pl(doc):

    doc.add_root(
            row(sel_month)
            )
        
    return pl


show(pl)

Output with jupyterlab 4.3.5 & dark theme:

2025-04-04 13_41_37-bokeh_custom… (2) - JupyterLab375×526 7.66 KB

Unfortunately I know next to nothing about HTML & CSS - problem #1. Suspect/hope there’s an easy solution - patient guidance much appreciated

Thanks!

Bokeh elements all live in a shadow DOM so need e.g. :host to target. Here is an example you can follow (I would suggest using Bokeh’s various stylesheet options as in that example)

bokeh/examples/styling/dom/css_classes.py at branch-3.8 · bokeh/bokeh · GitHub

Thank you very much Bryan! Took a minute to try this, but it ~worked with an InlineStyleSheet as in the example.

Just one followup question: which CSS property modifies the text color of the items in the widget (e.g. the Select in the example above)? color changes the text color of the Title, but not the items.

For a Select, I assume there are two properties; one for the default, one for when an item has mouse focus/is hovered over.

I’m afraid I don’t know. I usually open up a browser’s dev tools and use the DOM inspector when I need to hunt for CSS targets.

Got it, thanks -

This ended up working for me:

months = list(pd.date_range(start='2024-01-01', periods=12, 
                                            freq='ME').strftime('%b'))

sel_month = Select(title='Select Month:', value='All', 
                      options=['All']+months, css_classes=['bokeh_widget'])

stylesheet = InlineStyleSheet(css='''
:host(.custom) {
    .bk-input {
        color: black;
        };
''')

sel_month.css_classes = ['custom']
sel_month.stylesheets = [stylesheet]

layout = row(sel_month)

Output now:

2025-05-05 23_10_48-bokeh_custom… (3) - JupyterLab258×540 8.72 KB

Yay!

Is there an easy way to add this custom CSS to all input widgets, or must that be done one-by-one?

Thanks!

I believe that using GlobalInlineStyleSheet instead of InlineStyleSheet should accomplish that.

Thanks Bryan - that seems like it’s exactly what I’d want, but I could not get it to work.

Based on this post, it sounds like GlobalInlineStyleSheet may not work…

Best workaround I’ve been able to come up with is to define a collection of widgets and then loop through those with a function that sets the stylesheets and css_classes properties of each widget. Bit clunky, but does the trick…

(I also again tried to define something in jupyter’s custom_css, but that also didn’t work - probably because of the :host thingy )

Thanks again for all your help!

Based on this post, it sounds like GlobalInlineStyleSheet may not work…

Well, GlobalInlineStyleSheet normally appends to <head> I can imagine there could be some problem in the context of a Jupyter notebook, specifically. I’d suggest trying things outside the notebook with plain HTML (i.e. output_file) output. Then submitting a GitHub Issue with details.

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