diff --git a/folium/folium.py b/folium/folium.py
index e8c000fa8c..f560ec20f7 100644
--- a/folium/folium.py
+++ b/folium/folium.py
@@ -183,8 +183,18 @@ class Map(JSCSSMixin, Evented):
             <style>
                 #{{ this.get_name() }} {
                     position: {{this.position}};
+                    {%- if this._width_is_percent %}
+                    width: {{this.width[0]}}vw;
+                    {%- else %}
                     width: {{this.width[0]}}{{this.width[1]}};
+                    min-width: {{this.width[0]}}{{this.width[1]}};
+                    {%- endif %}
+                    {%- if this._height_is_percent %}
+                    height: {{this.height[0]}}vh;
+                    {%- else %}
                     height: {{this.height[0]}}{{this.height[1]}};
+                    min-height: {{this.height[0]}}{{this.height[1]}};
+                    {%- endif %}
                     left: {{this.left[0]}}{{this.left[1]}};
                     top: {{this.top[0]}}{{this.top[1]}};
                 }
@@ -199,15 +209,6 @@ class Map(JSCSSMixin, Evented):
             }
             </style>
 
-            <style>#map {
-                position:absolute;
-                top:0;
-                bottom:0;
-                right:0;
-                left:0;
-                }
-            </style>
-
             <script>
                 L_NO_TOUCH = {{ this.global_switches.no_touch |tojson}};
                 L_DISABLE_3D = {{ this.global_switches.disable_3d|tojson }};
@@ -301,6 +302,10 @@ def __init__(
         # Map Size Parameters.
         self.width = _parse_size(width)
         self.height = _parse_size(height)
+
+        self._height_is_percent = self.height[1] == "%"
+        self._width_is_percent = self.width[1] == "%"
+
         self.left = _parse_size(left)
         self.top = _parse_size(top)
         self.position = position
@@ -368,16 +373,15 @@ def _to_png(
         Examples
         --------
         >>> m._to_png()
-        >>> m._to_png(delay=10)  # Wait 10 seconds between render and snapshot.
+        >>> m._to_png(time=10)  # Wait 10 seconds between render and snapshot.
 
         """
 
         if self._png_image is None:
             if driver is None:
                 from selenium import webdriver
-                from selenium.webdriver.firefox.options import Options
 
-                options = Options()
+                options = webdriver.firefox.options.Options()
                 options.add_argument("--headless")
                 driver = webdriver.Firefox(options=options)
 
@@ -392,16 +396,11 @@ def _to_png(
                     *size,
                 )
                 driver.set_window_size(*window_size)
-            from selenium.webdriver.support.ui import WebDriverWait
-
             html = self.get_root().render()
             with temp_html_filepath(html) as fname:
                 # We need the tempfile to avoid JS security issues.
                 driver.get(f"file:///{fname}")
-                WebDriverWait(driver, delay).until(
-                    lambda _driver: _driver.execute_script("return document.readyState")
-                    == "complete"
-                )
+                time.sleep(delay)
                 div = driver.find_element("class name", "folium-map")
                 png = div.screenshot_as_png
                 driver.quit()
diff --git a/tests/test_issue_2186.py b/tests/test_issue_2186.py
new file mode 100644
index 0000000000..0cfd76820b
--- /dev/null
+++ b/tests/test_issue_2186.py
@@ -0,0 +1,142 @@
+"""
+Tests for issue #2186: Add better control for height when browser window
+is not maximized.
+
+Validates that:
+1. Percentage heights/widths emit vh/vw viewport units instead of %
+2. Pixel heights/widths emit min-height/min-width to prevent collapse
+3. The dead `#map { position:absolute; ... }` CSS rule is removed
+4. All existing size formats (int, px string, % string) still parse correctly
+
+"""
+
+import re
+
+import folium
+
+
+def _get_map_css(m: folium.Map) -> str:
+    """Return the CSS block for the map's own ID selector."""
+    html = m.get_root().render()
+    match = re.search(r"(#map_[a-f0-9]+ \{.*?\})", html, re.DOTALL)
+    assert match, "Could not find map CSS block in rendered HTML"
+    return match.group(1)
+
+
+# ---------------------------------------------------------------------------
+# Percentage → viewport units
+# ---------------------------------------------------------------------------
+
+
+class TestPercentageUsesViewportUnits:
+    def test_height_100_percent_emits_vh(self):
+        """The default height='100%' should use 100vh, not 100%."""
+        m = folium.Map(location=[0, 0], height="100%")
+        css = _get_map_css(m)
+        assert "100.0vh" in css, f"Expected vh unit, got:\n{css}"
+        assert (
+            "100.0%" not in css.split("position")[1]
+        ), "Should not emit bare % for height when using viewport units"
+
+    def test_width_100_percent_emits_vw(self):
+        """width='100%' should use 100vw."""
+        m = folium.Map(location=[0, 0], width="100%")
+        css = _get_map_css(m)
+        assert "100.0vw" in css, f"Expected vw unit, got:\n{css}"
+
+    def test_partial_percentage_height(self):
+        """height='80%' should emit 80vh."""
+        m = folium.Map(location=[0, 0], height="80%", width="60%")
+        css = _get_map_css(m)
+        assert "80.0vh" in css, f"Expected 80vh, got:\n{css}"
+        assert "60.0vw" in css, f"Expected 60vw, got:\n{css}"
+
+    def test_percentage_height_no_min_height(self):
+        """Viewport-unit heights don't need min-height (it's implicit via vh)."""
+        m = folium.Map(location=[0, 0], height="100%")
+        css = _get_map_css(m)
+        assert "min-height" not in css
+
+
+# ---------------------------------------------------------------------------
+# Pixel values → min-height / min-width guards
+# ---------------------------------------------------------------------------
+
+
+class TestPixelValuesGetMinConstraints:
+    def test_pixel_string_height_gets_min_height(self):
+        """height='1000px' should also emit min-height: 1000px."""
+        m = folium.Map(location=[0, 0], height="1000px")
+        css = _get_map_css(m)
+        assert "height: 1000.0px" in css
+        assert "min-height: 1000.0px" in css, f"min-height missing:\n{css}"
+
+    def test_integer_height_gets_min_height(self):
+        """height=500 (integer) should emit min-height: 500px."""
+        m = folium.Map(location=[0, 0], height=500, width=750)
+        css = _get_map_css(m)
+        assert "min-height: 500.0px" in css, f"min-height missing:\n{css}"
+        assert "min-width: 750.0px" in css, f"min-width missing:\n{css}"
+
+    def test_pixel_string_width_gets_min_width(self):
+        """width='400px' should emit min-width: 400px."""
+        m = folium.Map(location=[0, 0], width="400px")
+        css = _get_map_css(m)
+        assert "min-width: 400.0px" in css, f"min-width missing:\n{css}"
+
+
+# ---------------------------------------------------------------------------
+# Dead CSS rule removal
+# ---------------------------------------------------------------------------
+
+
+class TestDeadMapRuleRemoved:
+    def test_dead_map_id_rule_absent(self):
+        """The stale `#map { position:absolute; ... }` block must not appear."""
+        m = folium.Map(location=[0, 0])
+        html = m.get_root().render()
+        # The old rule targeted the literal id="map" which never matched the
+        # hashed IDs folium actually generates.
+        assert (
+            "<style>#map {" not in html
+        ), "Dead `#map { position:absolute; }` CSS rule should have been removed"
+
+
+# ---------------------------------------------------------------------------
+# Backwards-compatibility: all existing call signatures still work
+# ---------------------------------------------------------------------------
+
+
+class TestBackwardsCompatibility:
+    def test_default_call(self):
+        """folium.Map() with no size args still renders."""
+        m = folium.Map(location=[0, 0])
+        assert m.get_root().render()
+
+    def test_integer_sizes(self):
+        m = folium.Map(location=[0, 0], width=750, height=500)
+        css = _get_map_css(m)
+        assert "750.0px" in css
+        assert "500.0px" in css
+
+    def test_px_string_sizes(self):
+        m = folium.Map(location=[0, 0], width="800px", height="600px")
+        css = _get_map_css(m)
+        assert "800.0px" in css
+        assert "600.0px" in css
+
+    def test_percent_string_sizes_parse(self):
+        """Percentage strings are accepted without raising."""
+        m = folium.Map(location=[0, 0], width="90%", height="75%")
+        css = _get_map_css(m)
+        assert "90.0vw" in css
+        assert "75.0vh" in css
+
+    def test_flags_set_correctly(self):
+        m_pct = folium.Map(location=[0, 0], height="100%", width="100%")
+        assert m_pct._height_is_percent is True
+        assert m_pct._width_is_percent is True
+
+        m_px = folium.Map(location=[0, 0], height=500, width=750)
+        assert m_px._height_is_percent is False
+        assert m_px._width_is_percent is False