[williambdean]

Summary

The docs site currently has no favicon: docs/conf.py was scaffolded by
sphinx-quickstart in 2013 and the html_favicon option has sat
commented out ever since.

This PR adds a favicon so the browser tab shows the folium leaf instead
of a generic page icon:

• docs/_static/favicon.ico: the existing leaf logo centered on a
  square transparent canvas, exported at 16, 32, and 48 px
• docs/conf.py: set html_favicon = "_static/favicon.ico"

Details

The source folium_logo.png is 100x180 (and non-square), so it can't be
used directly. The favicon pads it to a 180x180 transparent square
rather than cropping, to keep the full leaf shape.

html_favicon accepts the path relative to the source directory;
pydata-sphinx-theme emits the <link rel="icon"> tag, and the file is
picked up through the existing html_static_path = ["_static"]
setting.

Verified locally: full make html build succeeds and the built
index.html contains <link rel="icon" href="_static/favicon.ico"/>.

Script used to generate favicon.ico from folium_logo.png

Ran once with uv run (script has inline PEP 723 deps); the output
favicon.ico is committed, so the script isn't part of the repo.

# /// script
# requires-python = ">=3.10"
# dependencies = ["pillow>=10"]
# ///
"""Build favicon.ico: the folium leaf centered on a transparent
square."""

from pathlib import Path

from PIL import Image

HERE = Path(__file__).parent
logo = Image.open(HERE / "folium_logo.png").convert("RGBA")

# Center the 100x180 leaf on a square transparent canvas.
w, h = logo.size
pad = (h - w) // 2
square = Image.new("RGBA", (h, h), (0, 0, 0, 0))
square.paste(logo, (pad, 0))

square.save(HERE / "favicon.ico", sizes=[(16, 16), (32, 32), (48, 48)])
print("wrote favicon.ico")

[hansthen]

@williambdean Again, thanks!