Vendor a glyphicons-only stylesheet instead of the full Bootstrap 3 base

[adarshsm]

Closes #1820. Thanks @hansthen for the steer.

folium loads netdna's bootstrap-glyphicons.css for the Awesome Markers glyphicon font. Despite the name, that file is a full Bootstrap 3 base stylesheet — alongside the @font-face/.glyphicon rules it ships a normalize reset and global body rules (font, colour, background, margin). Loaded after Bootstrap 5, those body rules leak onto the host page and, for example, mis-position a user-added Bootstrap 5 modal (the original report).

This vendors folium/templates/glyphicons.css containing only the @font-face and .glyphicon/.glyphicon-* rules (fonts served from jsDelivr), referenced the same way as the existing leaflet.awesome.rotate.css. Icon(prefix="glyphicon") markers keep working exactly as before; the page-wide body/reset pollution is gone.

Not a customer-facing change — glyphicon markers are unaffected; the only difference is that folium stops overriding the host page's body styles. Added a regression test asserting the vendored file is used and the netdna URL is gone.

[adarshsm]

Pushed a follow-up that should fix the failing snapshot job.

What was wrong: the vendored stylesheet was linked from cdn.jsdelivr.net/gh/python-visualization/folium/folium/templates/glyphicons.css, which jsDelivr serves from the default branch — so it 404s until this PR is merged (curl → HTTP 404). In CI the .glyphicon rules never load, and for a released package the URL would also point at a mutable main. It's the same /gh pattern awesome_rotate_css uses, but that file already exists on main; a brand-new vendored file can't resolve that way pre-merge.

Fix (59a744c): inline the glyphicons-only rules into every Map as a <style> block, read once from the packaged folium/templates/glyphicons.css. No external stylesheet request, no chicken-and-egg, and it keeps the GH-1820 goal (no Bootstrap-3 body reset leaking onto the host page). The glyph font still loads from the stable bootstrap@3.3.7 npm files (HTTP 200). Locally: 23 test_folium.py tests pass, black/ruff clean, and glyphicon markers render (icon classes map to the inlined .glyphicon-* rules).

One thing that still needs doing: the 7 snapshot baselines legitimately change, because dropping the leaked Bootstrap body-reset alters rendering even for non-glyphicon maps (e.g. issue_1885). Those need regenerating from the CI Ubuntu/Chrome environment. The workflows on my latest push are sitting in action_required — if a maintainer approves the run, I'll grab the screenshots artifact, sanity-check the renders, and commit them as the updated baselines.

[adarshsm]

CI is fixed in 9d24e8d, and the cause is worth a look before merging.

The snapshots were failing for a real reason, not a rendering fluke. All seven failed, and the pixel diffs are confined to text: Leaflet's attribution in the corner and, on issue_1989, branca's colorbar caption and tick labels. The map tiles, polygons, markers and controls are pixel-identical. The glyphicons themselves render fine.

The old netdna stylesheet was not glyphicons-only — it carried a full Bootstrap 3 reset, and among it:

html{font-size:62.5%;}
body{font-family:"Helvetica Neue",Helvetica,Arial,sans-serif;font-size:14px;...}
*,*:before,*:after{box-sizing:border-box;}

html{font-size:62.5%} makes 1rem = 10px instead of 16px. Leaflet 1.9 sizes the attribution control in rem, and branca's colorbar text inherits, so both were rendering about a third smaller than either library intends. Dropping the reset restores them to their own sizes — that is the entire visual delta.

So this is the leak from GH-1820 showing up on the map's own page too, not only on the host page embedding it. The old screenshots recorded the shrunken text; the new ones record what Leaflet and branca ask for.

I took the replacement screenshots from the CI artifact of the run against 59a744c (ubuntu-latest), so they come from the same environment that compares them rather than from my machine.

One thing to flag explicitly since it is your call, not mine: this makes the attribution and colorbar text slightly larger in every map, not just the one in the issue. I think that is correct — folium should not be resizing its own root font — but it is a visible change for existing users, so say the word if you would rather scope the stylesheet differently.