diff --git a/remarkbox/__init__.py b/remarkbox/__init__.py
index 6551a7e..ab9811b 100644
--- a/remarkbox/__init__.py
+++ b/remarkbox/__init__.py
@@ -99,6 +99,8 @@ def load_entry_points(group_name):
 def load_jinja2_themes(config):
     """Automatically load any entry_point registered Remarkbox theme."""
     themes = load_entry_points("remarkbox.themes")
+    theme_defaults = {}
+
     for theme_name, theme_module in themes.items():
         theme_module_name = theme_module.__name__
         # teach Jinja2 about the template dir in the theme package.
@@ -111,6 +113,12 @@ def load_jinja2_themes(config):
             "{}:static/theme/{}".format(theme_module_name, theme_name),
             cache_max_age=3600,
         )
+        # Collect theme's default mode if defined
+        if hasattr(theme_module, 'default_theme_mode'):
+            theme_defaults[theme_name] = theme_module.default_theme_mode
+
+    # Store theme defaults in config registry for later access
+    config.registry.settings['theme_defaults'] = theme_defaults
     return config
 
 
@@ -492,6 +500,30 @@ def main(global_config, **settings):
     def add_mathjax(request):
         return "true" if request.namespace.mathjax else "false"
 
+    def add_theme_mode(request):
+        """
+        Return theme mode 'light' or 'dark'.
+        Priority: user preference > query params > theme default > 'light'.
+        """
+        # If user is authenticated and has a preference
+        if request.user and request.user.authenticated and request.user.theme_mode != 'auto':
+            return request.user.theme_mode
+
+        # Check if there's a mode parameter (for embeds or overrides)
+        param_mode = request.params.get("mode")
+        if param_mode in ("light", "dark"):
+            return param_mode
+
+        # Use theme's default mode if available
+        if request.theme:
+            theme_defaults = request.registry.settings.get('theme_defaults', {})
+            theme_default = theme_defaults.get(request.theme)
+            if theme_default in ("light", "dark"):
+                return theme_default
+
+        # Final fallback to light
+        return "light"
+
     # register functions to app config as request methods.
     # each request instance will run these functions and attach results.
     # cache result with `reify=True` to prevent multiple db lookups.
@@ -546,6 +578,7 @@ def main(global_config, **settings):
     config.add_request_method(add_page_offset, "page_offset", reify=True)
     config.add_request_method(add_node_order, "node_order", reify=True)
     config.add_request_method(add_mathjax, "mathjax", reify=True)
+    config.add_request_method(add_theme_mode, "theme_mode", reify=True)
 
     # all of the web application routes.
     config.include(".routes")
diff --git a/remarkbox/models/user.py b/remarkbox/models/user.py
index 3865e45..1e194d3 100644
--- a/remarkbox/models/user.py
+++ b/remarkbox/models/user.py
@@ -114,6 +114,12 @@ class User(RBase, Base):
         default="daily",
         nullable=False,
     )
+    # Theme mode preference: 'auto', 'light', or 'dark'. 'auto' respects parent site.
+    theme_mode = Column(
+        Enum('auto', 'light', 'dark', name='theme_mode_enum'),
+        default='auto',
+        nullable=False,
+    )
     # example: cus_12345678AbCdEF but may be null.
     stripe_id = Column(Unicode(18), unique=True, nullable=True)
 
diff --git a/remarkbox/scripts/alembic/versions/add_theme_mode_to_user.py b/remarkbox/scripts/alembic/versions/add_theme_mode_to_user.py
new file mode 100644
index 0000000..724cc09
--- /dev/null
+++ b/remarkbox/scripts/alembic/versions/add_theme_mode_to_user.py
@@ -0,0 +1,34 @@
+"""add theme_mode column to rb_user
+
+Revision ID: b8f3c9d4e5a1
+Revises: 14a6a35940c7
+Create Date: 2025-10-11 00:00:00.000000
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = 'b8f3c9d4e5a1'
+down_revision = '14a6a35940c7'
+branch_labels = None
+depends_on = None
+
+from alembic import op
+import sqlalchemy as sa
+
+
+def upgrade():
+    op.add_column(
+        'rb_user',
+        sa.Column(
+            'theme_mode',
+            sa.Enum('auto', 'light', 'dark', name='theme_mode_enum'),
+            nullable=False,
+            server_default='auto',
+        ),
+    )
+
+
+def downgrade():
+    op.drop_column('rb_user', 'theme_mode')
+    # Also drop the enum type
+    op.execute('DROP TYPE theme_mode_enum')
diff --git a/remarkbox/static/css/common.css b/remarkbox/static/css/common.css
index 40bf713..ebc86be 100644
--- a/remarkbox/static/css/common.css
+++ b/remarkbox/static/css/common.css
@@ -1,10 +1,11 @@
-/* Variables */
+/* Variables - Light Mode (default) */
 :root {
   --color: #222222;
   --color-muted: #3f3f3f;
 
   --color-code: #000000;
 
+  --background: #ffffff;
   --background-faint: #fafafa;
 
   --primary: #d40000; /* Remarkbox logo color */
@@ -19,6 +20,28 @@
   --line-height: 1.6;
 }
 
+/* Dark Mode Variables */
+:root.dark-mode {
+  --color: #e8e8e8;
+  --color-muted: #b0b0b0;
+
+  --color-code: #e8e8e8;
+
+  --background: #1a1a1a;
+  --background-faint: #2a2a2a;
+
+  --primary: #ff5555; /* Brighter red for dark mode */
+  --primary-hover: #ff7777;
+  --primary-inverse: #1a1a1a;
+
+  --border: #444444;
+  --border-faint: #333333;
+
+  --color-mod: #ff5555;
+
+  --line-height: 1.6;
+}
+
 body {
   overflow-x: hidden;
   line-height: var(--line-height);
@@ -26,6 +49,7 @@ body {
   font-family: "Raleway", "HelveticaNeue", "Helvetica Neue", Helvetica, Arial,
     sans-serif;
   color: var(--color);
+  background-color: var(--background);
 }
 
 h1,
diff --git a/remarkbox/templates/base.j2 b/remarkbox/templates/base.j2
index 766d105..10f8a1c 100644
--- a/remarkbox/templates/base.j2
+++ b/remarkbox/templates/base.j2
@@ -1,7 +1,7 @@
 {%- import 'snippets/snippets.j2' as snippets with context -%}
 {% include 'snippets/owner-key-comment.j2' %}
 <!DOCTYPE html>
-<html lang="en">
+<html lang="en" class="{% if request.theme_mode == 'dark' %}dark-mode{% endif %}">
 <head>
   <title>{% block title %}{{ request.app_domain }}{% endblock %}</title>
   <meta charset="utf-8" />
diff --git a/remarkbox/templates/embed-iframe.txt.j2 b/remarkbox/templates/embed-iframe.txt.j2
index 5f44edf..d2dfc26 100644
--- a/remarkbox/templates/embed-iframe.txt.j2
+++ b/remarkbox/templates/embed-iframe.txt.j2
@@ -1,7 +1,7 @@
 <!-- Remarkbox - Your readers want to communicate with you -->
 <div id="remarkbox-div">
   <noscript>
-    <iframe id=remarkbox-iframe src="{{ request.scheme }}://{{ request.host }}/embed?nojs=true" style="height:600px;width:100%;border:none!important" tabindex=0></iframe>
+    <iframe id=remarkbox-iframe src="{{ request.scheme }}://{{ request.host }}/embed?nojs=true&mode={{ mode }}" style="height:600px;width:100%;border:none!important" tabindex=0></iframe>
   </noscript>
 </div>
 <script src="{{ request.scheme }}://{{ request.host }}/static/js/iframe-resizer/iframeResizer.min.js"></script>
@@ -12,10 +12,11 @@
   var thread_fragment = window.location.hash;
 
   // rb owner was here.
-  var rb_src = "{{ request.scheme }}://{{ request.host }}/embed" + 
+  var rb_src = "{{ request.scheme }}://{{ request.host }}/embed" +
       "?rb_owner_key=" + rb_owner_key +
       "&thread_title=" + encodeURI(thread_title) +
-      "&thread_uri=" + encodeURIComponent(thread_uri) + 
+      "&thread_uri=" + encodeURIComponent(thread_uri) +
+      "&mode={{ mode }}" +
       thread_fragment;
 
   function create_remarkbox_iframe() {
diff --git a/remarkbox/templates/user-settings.j2 b/remarkbox/templates/user-settings.j2
index d3d3382..5e89141 100644
--- a/remarkbox/templates/user-settings.j2
+++ b/remarkbox/templates/user-settings.j2
@@ -29,12 +29,9 @@
 
 {{ snippets.user_avatar_link(request.user, 130, class="user-settings-profile-pic") }}
 <br>
-<br>
 
 <input type="checkbox" name="gravatar-checkbox" id="gravatar-checkbox" {% if request.user.gravatar %}checked{% endif %}></input> enable <a href="https://en.gravatar.com/support/what-is-gravatar/" target="_blank">gravatar</a>?
 
-<br/>
-<br/>
 <br/>
 
 <!--
@@ -52,6 +49,19 @@ automatically watch any threads I participate in.
 
 -->
 
+<br/>
+<label>Theme Mode</label>
+
+<div class="theme-appearance-section">
+<input type="radio" name="theme-mode" id="theme-mode-auto" value="auto" {% if request.user.theme_mode == "auto" %}checked{% endif %} onchange="previewTheme(this.value)"></input> <label for="theme-mode-auto" class="inline-label">Auto (follow parent site)</label>
+<br/>
+<input type="radio" name="theme-mode" id="theme-mode-light" value="light" {% if request.user.theme_mode == "light" %}checked{% endif %} onchange="previewTheme(this.value)"></input> <label for="theme-mode-light" class="inline-label">Light</label>
+<br/>
+<input type="radio" name="theme-mode" id="theme-mode-dark" value="dark" {% if request.user.theme_mode == "dark" %}checked{% endif %} onchange="previewTheme(this.value)"></input> <label for="theme-mode-dark" class="inline-label">Dark</label>
+</div>
+
+<br/>
+
 <label>Reply Notifications</label>
 
 When my comments get a reply, notify me
@@ -95,4 +105,25 @@ View and adjust your <a href="{{ request.link_prefix }}/u/watching">Namespace no
 
 </form>
 
+<script>
+function previewTheme(mode) {
+  const html = document.documentElement;
+
+  if (mode === 'dark') {
+    html.classList.add('dark-mode');
+  } else if (mode === 'light') {
+    html.classList.remove('dark-mode');
+  } else if (mode === 'auto') {
+    // Auto mode: check if parent provided a mode parameter
+    const urlParams = new URLSearchParams(window.location.search);
+    const parentMode = urlParams.get('mode');
+    if (parentMode === 'dark') {
+      html.classList.add('dark-mode');
+    } else {
+      html.classList.remove('dark-mode');
+    }
+  }
+}
+</script>
+
 {%- endblock -%}
diff --git a/remarkbox/views/authenticated/authenticated.py b/remarkbox/views/authenticated/authenticated.py
index 2c25197..39067e4 100644
--- a/remarkbox/views/authenticated/authenticated.py
+++ b/remarkbox/views/authenticated/authenticated.py
@@ -231,6 +231,7 @@ def user_settings(request):
         default_node_watcher_frequency = request.params[
             "default-node-watcher-frequency"
         ]
+        theme_mode = request.params.get("theme-mode", "auto")
 
         if display_name != request.user.name:
             if is_user_name_valid(display_name) == False:
@@ -324,6 +325,25 @@ def user_settings(request):
                     ("Invalid Enum value for reply_watcher_frequency.", "error")
                 )
 
+        if theme_mode != request.user.theme_mode:
+            if theme_mode in ('auto', 'light', 'dark'):
+                request.user.theme_mode = theme_mode
+                theme_labels = {
+                    'auto': 'Auto (follow parent site)',
+                    'light': 'Light',
+                    'dark': 'Dark'
+                }
+                request.session.flash(
+                    (
+                        "Theme appearance set to <b>{}</b>".format(theme_labels[theme_mode]),
+                        "success",
+                    )
+                )
+            else:
+                request.session.flash(
+                    ("Invalid theme mode value.", "error")
+                )
+
         request.dbsession.add(request.user)
         request.dbsession.flush()
 
diff --git a/remarkbox/views/misc.py b/remarkbox/views/misc.py
index 3133f5d..c2af0e7 100644
--- a/remarkbox/views/misc.py
+++ b/remarkbox/views/misc.py
@@ -92,7 +92,10 @@ def show_count(request):
 @view_config(route_name="embed-iframe-min")
 def embed_iframe(request):
     """Jinja render a text file and serve it as plain text."""
-    context = {"rb_owner_key": request.params.get("rb_owner_key", "none")}
+    context = {
+        "rb_owner_key": request.params.get("rb_owner_key", "none"),
+        "mode": request.params.get("mode", "light")
+    }
     response = render_to_response("embed-iframe.txt.j2", context, request=request)
     response.content_type = "text/plain"
     if request.matched_route.name == "embed-iframe-min":