diff --git a/folium/folium.py b/folium/folium.py
index 8983ce2721..658837d3b6 100644
--- a/folium/folium.py
+++ b/folium/folium.py
@@ -6,6 +6,7 @@
 import time
 import webbrowser
 from collections.abc import Sequence
+from importlib.resources import files as _resource_files
 from typing import Any, Optional, Union
 
 from branca.element import Element, Figure
@@ -43,11 +44,12 @@
         "bootstrap_css",
         "https://cdn.jsdelivr.net/npm/bootstrap@5.2.2/dist/css/bootstrap.min.css",
     ),
-    # glyphicons came from Bootstrap 3 and are used for Awesome Markers
-    (
-        "glyphicons_css",
-        "https://netdna.bootstrapcdn.com/bootstrap/3.0.0/css/bootstrap-glyphicons.css",
-    ),
+    # glyphicons (used for the default Awesome Markers) are inlined into every
+    # ``Map`` as a ``<style>`` block from ``_GLYPHICONS_CSS`` below, rather than
+    # linked from a CDN. The previous netdna stylesheet shipped a full
+    # Bootstrap-3 reset that leaked global ``body`` styles onto the host page
+    # (GH-1820); inlining a glyphicons-only sheet keeps markers working with no
+    # page-wide side effects and no external stylesheet request.
     (
         "awesome_markers_font_css",
         "https://cdn.jsdelivr.net/npm/@fortawesome/fontawesome-free@6.2.0/css/all.min.css",
@@ -62,6 +64,13 @@
     ),  # noqa
 ]
 
+# Glyphicons-only stylesheet inlined into every ``Map`` (see the note in
+# ``_default_css``). Read once from the packaged template; the file ships via
+# ``recursive-include folium/templates`` in ``MANIFEST.in``.
+_GLYPHICONS_CSS = (
+    _resource_files("folium") / "templates" / "glyphicons.css"
+).read_text(encoding="utf-8")
+
 
 class GlobalSwitches(Element):
     _template = Template("""
@@ -219,6 +228,8 @@ class Map(JSCSSMixin, Evented):
                 }
             </style>
 
+            <style>{{ this.glyphicons_css }}</style>
+
             <script>
                 L_NO_TOUCH = {{ this.global_switches.no_touch |tojson}};
                 L_DISABLE_3D = {{ this.global_switches.disable_3d|tojson }};
@@ -266,6 +277,9 @@ class Map(JSCSSMixin, Evented):
     default_js = _default_js
     default_css = _default_css
 
+    # Inlined into the map header as a ``<style>`` block (see ``_GLYPHICONS_CSS``).
+    glyphicons_css = _GLYPHICONS_CSS
+
     def __init__(
         self,
         location: Optional[Sequence[float]] = None,
diff --git a/folium/templates/glyphicons.css b/folium/templates/glyphicons.css
new file mode 100644
index 0000000000..f0ac109cda
--- /dev/null
+++ b/folium/templates/glyphicons.css
@@ -0,0 +1,211 @@
+/*
+ * Glyphicons Halflings -- the icon font used by folium's default Awesome Markers
+ * (Icon(prefix="glyphicon")). Extracted from Bootstrap 3's glyphicon rules only.
+ *
+ * folium previously loaded netdna's bootstrap-glyphicons.css, which despite its
+ * name ships a full Bootstrap-3 base stylesheet (normalize reset + global `body`
+ * rules) that leaked onto the host page (GH-1820). This file provides just the
+ * @font-face and .glyphicon/.glyphicon-* rules needed for the markers, with no
+ * page-wide side effects. Font files are served from jsDelivr.
+ */
+@font-face{font-family:'Glyphicons Halflings';src:url('https://cdn.jsdelivr.net/npm/bootstrap@3.3.7/fonts/glyphicons-halflings-regular.eot');src:url('https://cdn.jsdelivr.net/npm/bootstrap@3.3.7/fonts/glyphicons-halflings-regular.eot?#iefix') format('embedded-opentype'),url('https://cdn.jsdelivr.net/npm/bootstrap@3.3.7/fonts/glyphicons-halflings-regular.woff') format('woff'),url('https://cdn.jsdelivr.net/npm/bootstrap@3.3.7/fonts/glyphicons-halflings-regular.ttf') format('truetype'),url('https://cdn.jsdelivr.net/npm/bootstrap@3.3.7/fonts/glyphicons-halflings-regular.svg#glyphicons-halflingsregular') format('svg');}.glyphicon{position:relative;top:1px;display:inline-block;font-family:'Glyphicons Halflings';font-style:normal;font-weight:normal;line-height:1;-webkit-font-smoothing:antialiased;}
+.glyphicon-asterisk:before{content:"\2a";}
+.glyphicon-plus:before{content:"\2b";}
+.glyphicon-euro:before{content:"\20ac";}
+.glyphicon-minus:before{content:"\2212";}
+.glyphicon-cloud:before{content:"\2601";}
+.glyphicon-envelope:before{content:"\2709";}
+.glyphicon-pencil:before{content:"\270f";}
+.glyphicon-glass:before{content:"\e001";}
+.glyphicon-music:before{content:"\e002";}
+.glyphicon-search:before{content:"\e003";}
+.glyphicon-heart:before{content:"\e005";}
+.glyphicon-star:before{content:"\e006";}
+.glyphicon-star-empty:before{content:"\e007";}
+.glyphicon-user:before{content:"\e008";}
+.glyphicon-film:before{content:"\e009";}
+.glyphicon-th-large:before{content:"\e010";}
+.glyphicon-th:before{content:"\e011";}
+.glyphicon-th-list:before{content:"\e012";}
+.glyphicon-ok:before{content:"\e013";}
+.glyphicon-remove:before{content:"\e014";}
+.glyphicon-zoom-in:before{content:"\e015";}
+.glyphicon-zoom-out:before{content:"\e016";}
+.glyphicon-off:before{content:"\e017";}
+.glyphicon-signal:before{content:"\e018";}
+.glyphicon-cog:before{content:"\e019";}
+.glyphicon-trash:before{content:"\e020";}
+.glyphicon-home:before{content:"\e021";}
+.glyphicon-file:before{content:"\e022";}
+.glyphicon-time:before{content:"\e023";}
+.glyphicon-road:before{content:"\e024";}
+.glyphicon-download-alt:before{content:"\e025";}
+.glyphicon-download:before{content:"\e026";}
+.glyphicon-upload:before{content:"\e027";}
+.glyphicon-inbox:before{content:"\e028";}
+.glyphicon-play-circle:before{content:"\e029";}
+.glyphicon-repeat:before{content:"\e030";}
+.glyphicon-refresh:before{content:"\e031";}
+.glyphicon-list-alt:before{content:"\e032";}
+.glyphicon-flag:before{content:"\e034";}
+.glyphicon-headphones:before{content:"\e035";}
+.glyphicon-volume-off:before{content:"\e036";}
+.glyphicon-volume-down:before{content:"\e037";}
+.glyphicon-volume-up:before{content:"\e038";}
+.glyphicon-qrcode:before{content:"\e039";}
+.glyphicon-barcode:before{content:"\e040";}
+.glyphicon-tag:before{content:"\e041";}
+.glyphicon-tags:before{content:"\e042";}
+.glyphicon-book:before{content:"\e043";}
+.glyphicon-print:before{content:"\e045";}
+.glyphicon-font:before{content:"\e047";}
+.glyphicon-bold:before{content:"\e048";}
+.glyphicon-italic:before{content:"\e049";}
+.glyphicon-text-height:before{content:"\e050";}
+.glyphicon-text-width:before{content:"\e051";}
+.glyphicon-align-left:before{content:"\e052";}
+.glyphicon-align-center:before{content:"\e053";}
+.glyphicon-align-right:before{content:"\e054";}
+.glyphicon-align-justify:before{content:"\e055";}
+.glyphicon-list:before{content:"\e056";}
+.glyphicon-indent-left:before{content:"\e057";}
+.glyphicon-indent-right:before{content:"\e058";}
+.glyphicon-facetime-video:before{content:"\e059";}
+.glyphicon-picture:before{content:"\e060";}
+.glyphicon-map-marker:before{content:"\e062";}
+.glyphicon-adjust:before{content:"\e063";}
+.glyphicon-tint:before{content:"\e064";}
+.glyphicon-edit:before{content:"\e065";}
+.glyphicon-share:before{content:"\e066";}
+.glyphicon-check:before{content:"\e067";}
+.glyphicon-move:before{content:"\e068";}
+.glyphicon-step-backward:before{content:"\e069";}
+.glyphicon-fast-backward:before{content:"\e070";}
+.glyphicon-backward:before{content:"\e071";}
+.glyphicon-play:before{content:"\e072";}
+.glyphicon-pause:before{content:"\e073";}
+.glyphicon-stop:before{content:"\e074";}
+.glyphicon-forward:before{content:"\e075";}
+.glyphicon-fast-forward:before{content:"\e076";}
+.glyphicon-step-forward:before{content:"\e077";}
+.glyphicon-eject:before{content:"\e078";}
+.glyphicon-chevron-left:before{content:"\e079";}
+.glyphicon-chevron-right:before{content:"\e080";}
+.glyphicon-plus-sign:before{content:"\e081";}
+.glyphicon-minus-sign:before{content:"\e082";}
+.glyphicon-remove-sign:before{content:"\e083";}
+.glyphicon-ok-sign:before{content:"\e084";}
+.glyphicon-question-sign:before{content:"\e085";}
+.glyphicon-info-sign:before{content:"\e086";}
+.glyphicon-screenshot:before{content:"\e087";}
+.glyphicon-remove-circle:before{content:"\e088";}
+.glyphicon-ok-circle:before{content:"\e089";}
+.glyphicon-ban-circle:before{content:"\e090";}
+.glyphicon-arrow-left:before{content:"\e091";}
+.glyphicon-arrow-right:before{content:"\e092";}
+.glyphicon-arrow-up:before{content:"\e093";}
+.glyphicon-arrow-down:before{content:"\e094";}
+.glyphicon-share-alt:before{content:"\e095";}
+.glyphicon-resize-full:before{content:"\e096";}
+.glyphicon-resize-small:before{content:"\e097";}
+.glyphicon-exclamation-sign:before{content:"\e101";}
+.glyphicon-gift:before{content:"\e102";}
+.glyphicon-leaf:before{content:"\e103";}
+.glyphicon-eye-open:before{content:"\e105";}
+.glyphicon-eye-close:before{content:"\e106";}
+.glyphicon-warning-sign:before{content:"\e107";}
+.glyphicon-plane:before{content:"\e108";}
+.glyphicon-random:before{content:"\e110";}
+.glyphicon-comment:before{content:"\e111";}
+.glyphicon-magnet:before{content:"\e112";}
+.glyphicon-chevron-up:before{content:"\e113";}
+.glyphicon-chevron-down:before{content:"\e114";}
+.glyphicon-retweet:before{content:"\e115";}
+.glyphicon-shopping-cart:before{content:"\e116";}
+.glyphicon-folder-close:before{content:"\e117";}
+.glyphicon-folder-open:before{content:"\e118";}
+.glyphicon-resize-vertical:before{content:"\e119";}
+.glyphicon-resize-horizontal:before{content:"\e120";}
+.glyphicon-hdd:before{content:"\e121";}
+.glyphicon-bullhorn:before{content:"\e122";}
+.glyphicon-certificate:before{content:"\e124";}
+.glyphicon-thumbs-up:before{content:"\e125";}
+.glyphicon-thumbs-down:before{content:"\e126";}
+.glyphicon-hand-right:before{content:"\e127";}
+.glyphicon-hand-left:before{content:"\e128";}
+.glyphicon-hand-up:before{content:"\e129";}
+.glyphicon-hand-down:before{content:"\e130";}
+.glyphicon-circle-arrow-right:before{content:"\e131";}
+.glyphicon-circle-arrow-left:before{content:"\e132";}
+.glyphicon-circle-arrow-up:before{content:"\e133";}
+.glyphicon-circle-arrow-down:before{content:"\e134";}
+.glyphicon-globe:before{content:"\e135";}
+.glyphicon-tasks:before{content:"\e137";}
+.glyphicon-filter:before{content:"\e138";}
+.glyphicon-fullscreen:before{content:"\e140";}
+.glyphicon-dashboard:before{content:"\e141";}
+.glyphicon-heart-empty:before{content:"\e143";}
+.glyphicon-link:before{content:"\e144";}
+.glyphicon-phone:before{content:"\e145";}
+.glyphicon-usd:before{content:"\e148";}
+.glyphicon-gbp:before{content:"\e149";}
+.glyphicon-sort:before{content:"\e150";}
+.glyphicon-sort-by-alphabet:before{content:"\e151";}
+.glyphicon-sort-by-alphabet-alt:before{content:"\e152";}
+.glyphicon-sort-by-order:before{content:"\e153";}
+.glyphicon-sort-by-order-alt:before{content:"\e154";}
+.glyphicon-sort-by-attributes:before{content:"\e155";}
+.glyphicon-sort-by-attributes-alt:before{content:"\e156";}
+.glyphicon-unchecked:before{content:"\e157";}
+.glyphicon-expand:before{content:"\e158";}
+.glyphicon-collapse-down:before{content:"\e159";}
+.glyphicon-collapse-up:before{content:"\e160";}
+.glyphicon-log-in:before{content:"\e161";}
+.glyphicon-flash:before{content:"\e162";}
+.glyphicon-log-out:before{content:"\e163";}
+.glyphicon-new-window:before{content:"\e164";}
+.glyphicon-record:before{content:"\e165";}
+.glyphicon-save:before{content:"\e166";}
+.glyphicon-open:before{content:"\e167";}
+.glyphicon-saved:before{content:"\e168";}
+.glyphicon-import:before{content:"\e169";}
+.glyphicon-export:before{content:"\e170";}
+.glyphicon-send:before{content:"\e171";}
+.glyphicon-floppy-disk:before{content:"\e172";}
+.glyphicon-floppy-saved:before{content:"\e173";}
+.glyphicon-floppy-remove:before{content:"\e174";}
+.glyphicon-floppy-save:before{content:"\e175";}
+.glyphicon-floppy-open:before{content:"\e176";}
+.glyphicon-credit-card:before{content:"\e177";}
+.glyphicon-transfer:before{content:"\e178";}
+.glyphicon-cutlery:before{content:"\e179";}
+.glyphicon-header:before{content:"\e180";}
+.glyphicon-compressed:before{content:"\e181";}
+.glyphicon-earphone:before{content:"\e182";}
+.glyphicon-phone-alt:before{content:"\e183";}
+.glyphicon-tower:before{content:"\e184";}
+.glyphicon-stats:before{content:"\e185";}
+.glyphicon-sd-video:before{content:"\e186";}
+.glyphicon-hd-video:before{content:"\e187";}
+.glyphicon-subtitles:before{content:"\e188";}
+.glyphicon-sound-stereo:before{content:"\e189";}
+.glyphicon-sound-dolby:before{content:"\e190";}
+.glyphicon-sound-5-1:before{content:"\e191";}
+.glyphicon-sound-6-1:before{content:"\e192";}
+.glyphicon-sound-7-1:before{content:"\e193";}
+.glyphicon-copyright-mark:before{content:"\e194";}
+.glyphicon-registration-mark:before{content:"\e195";}
+.glyphicon-cloud-download:before{content:"\e197";}
+.glyphicon-cloud-upload:before{content:"\e198";}
+.glyphicon-tree-conifer:before{content:"\e199";}
+.glyphicon-tree-deciduous:before{content:"\e200";}
+.glyphicon-briefcase:before{content:"\1f4bc";}
+.glyphicon-calendar:before{content:"\1f4c5";}
+.glyphicon-pushpin:before{content:"\1f4cc";}
+.glyphicon-paperclip:before{content:"\1f4ce";}
+.glyphicon-camera:before{content:"\1f4f7";}
+.glyphicon-lock:before{content:"\1f512";}
+.glyphicon-bell:before{content:"\1f514";}
+.glyphicon-bookmark:before{content:"\1f516";}
+.glyphicon-fire:before{content:"\1f525";}
+.glyphicon-wrench:before{content:"\1f527";}
diff --git a/tests/test_folium.py b/tests/test_folium.py
index 0947da1350..7679140c1e 100644
--- a/tests/test_folium.py
+++ b/tests/test_folium.py
@@ -53,6 +53,19 @@ def test_location_args():
     assert m.location == [45.5236, -122.6750]
 
 
+def test_glyphicons_css_is_vendored():
+    # GH-1820: the glyphicon rules must come from folium's inlined glyphicons-only
+    # stylesheet, not netdna's ``bootstrap-glyphicons.css`` which despite its name
+    # ships a full Bootstrap-3 reset that leaked global ``body`` styles onto the page.
+    m = folium.Map()
+    html = m.get_root().render()
+    # Inlined as a <style> block rather than linked from a CDN, so the glyphicon
+    # rules are present verbatim and no netdna stylesheet is requested.
+    assert "Glyphicons Halflings" in html
+    assert ".glyphicon" in html
+    assert "netdna.bootstrapcdn.com" not in html
+
+
 class TestFolium:
     """Test class for the Folium library."""