Fixed #33690 -- Added switch button for dark mode in the admin.

django/contrib/admin/static/admin/css/base.css

@@ -5,6 +5,7 @@
 @import url(fonts.css);
 
 /* VARIABLE DEFINITIONS */
+html[data-theme="light"],
 :root {
   --primary: #79aec8;
   --secondary: #417690;
@@ -900,7 +901,7 @@ a.deletelink:focus, a.deletelink:hover {
 }
 
 #branding {
-    float: left;
+    display: flex;
 }
 
 #branding h1 {

django/contrib/admin/static/admin/css/dark_mode.css

@@ -31,3 +31,87 @@
       --close-button-hover-bg: #666666;
     }
   }
+
+
+html[data-theme="dark"] {
+    --primary: #264b5d;
+    --primary-fg: #f7f7f7;
+
+    --body-fg: #eeeeee;
+    --body-bg: #121212;
+    --body-quiet-color: #e0e0e0;
+    --body-loud-color: #ffffff;
+
+    --breadcrumbs-link-fg: #e0e0e0;
+    --breadcrumbs-bg: var(--primary);
+
+    --link-fg: #81d4fa;
+    --link-hover-color: #4ac1f7;
+    --link-selected-fg: #6f94c6;
+
+    --hairline-color: #272727;
+    --border-color: #353535;
+
+    --error-fg: #e35f5f;
+    --message-success-bg: #006b1b;
+    --message-warning-bg: #583305;
+    --message-error-bg: #570808;
+
+    --darkened-bg: #212121;
+    --selected-bg: #1b1b1b;
+    --selected-row: #00363a;
+
+    --close-button-bg: #333333;
+    --close-button-hover-bg: #666666;
+}
+
+/* THEME SWITCH */
+.theme-toggle {
+    cursor: pointer;
+    border: none;
+    padding: 0;
+    background: transparent;
+    vertical-align: middle;
+    margin-left: 5px;
+    margin-top: -1px;
+}
+
+.theme-toggle svg {
+    vertical-align: middle;
+    height: 1rem;
+    width: 1rem;
+    display: none;
+}
+
+/* ICONS */
+.theme-toggle svg.theme-icon-when-auto,
+.theme-toggle svg.theme-icon-when-dark,
+.theme-toggle svg.theme-icon-when-light {
+    fill: var(--header-link-color);
+    color: var(--header-bg);
+}
+
+html[data-theme="auto"] .theme-toggle svg.theme-icon-when-auto {
+    display: block;
+}
+
+html[data-theme="dark"] .theme-toggle svg.theme-icon-when-dark {
+    display: block;
+}
+
+html[data-theme="light"] .theme-toggle svg.theme-icon-when-light {
+    display: block;
+}
+
+.visually-hidden {
+    position: absolute;
+    width: 1px;
+    height: 1px;
+    padding: 0;
+    overflow: hidden;
+    clip: rect(0,0,0,0);
+    white-space: nowrap;
+    border: 0;
+    color: var(--body-fg);
+    background-color: var(--body-bg);
+}

django/contrib/admin/static/admin/js/theme.js

@@ -0,0 +1,56 @@
+'use strict';
+{
+    window.addEventListener('load', function(e) {
+
+        function setTheme(mode) {
+            if (mode !== "light" && mode !== "dark" && mode !== "auto") {
+                console.error(`Got invalid theme mode: ${mode}. Resetting to auto.`);
+                mode = "auto";
+            }
+            document.documentElement.dataset.theme = mode;
+            localStorage.setItem("theme", mode);
+        }
+
+        function cycleTheme() {
+            const currentTheme = localStorage.getItem("theme") || "auto";
+            const prefersDark = window.matchMedia("(prefers-color-scheme: dark)").matches;
+
+            if (prefersDark) {
+                // Auto (dark) -> Light -> Dark
+                if (currentTheme === "auto") {
+                    setTheme("light");
+                } else if (currentTheme === "light") {
+                    setTheme("dark");
+                } else {
+                    setTheme("auto");
+                }
+            } else {
+                // Auto (light) -> Dark -> Light
+                if (currentTheme === "auto") {
+                    setTheme("dark");
+                } else if (currentTheme === "dark") {
+                    setTheme("light");
+                } else {
+                    setTheme("auto");
+                }
+            }
+        }
+
+        function initTheme() {
+            // set theme defined in localStorage if there is one, or fallback to auto mode
+            const currentTheme = localStorage.getItem("theme");
+            currentTheme ? setTheme(currentTheme) : setTheme("auto");
+        }
+
+        function setupTheme() {
+            // Attach event handlers for toggling themes
+            const buttons = document.getElementsByClassName("theme-toggle");
+            Array.from(buttons).forEach((btn) => {
+                btn.addEventListener("click", cycleTheme);
+            });
+            initTheme();
+        }
+
+        setupTheme();
+    });
+}

django/contrib/admin/templates/admin/base.html

@@ -6,6 +6,7 @@
 <link rel="stylesheet" href="{% block stylesheet %}{% static "admin/css/base.css" %}{% endblock %}">
 {% block dark-mode-vars %}
   <link rel="stylesheet" href="{% static "admin/css/dark_mode.css" %}">
+  <script src="{% static "admin/js/theme.js" %}" defer></script>
 {% endblock %}
 {% if not is_popup and is_nav_sidebar_enabled %}
   <link rel="stylesheet" href="{% static "admin/css/nav_sidebar.css" %}">
@@ -59,6 +60,7 @@
                     {% csrf_token %}
                     <button type="submit">{% translate 'Log out' %}</button>
                 </form>
+                {% include "admin/color_theme_toggle.html" %}
             {% endblock %}
         </div>
         {% endif %}
@@ -107,5 +109,13 @@
     </div>
 </div>
 <!-- END Container -->
+
+<!-- SVGs -->
+<svg xmlns="http://www.w3.org/2000/svg">
+  <symbol viewBox="0 0 24 24" width="16" height="16" id="icon-auto"><path d="M0 0h24v24H0z" fill="currentColor"/><path d="M12 22C6.477 22 2 17.523 2 12S6.477 2 12 2s10 4.477 10 10-4.477 10-10 10zm0-2V4a8 8 0 1 0 0 16z"/></symbol>
+  <symbol viewBox="0 0 24 24" width="16" height="16" id="icon-moon"><path d="M0 0h24v24H0z" fill="currentColor"/><path d="M10 7a7 7 0 0 0 12 4.9v.1c0 5.523-4.477 10-10 10S2 17.523 2 12 6.477 2 12 2h.1A6.979 6.979 0 0 0 10 7zm-6 5a8 8 0 0 0 15.062 3.762A9 9 0 0 1 8.238 4.938 7.999 7.999 0 0 0 4 12z"/></symbol>
+  <symbol viewBox="0 0 24 24" width="16" height="16" id="icon-sun"><path d="M0 0h24v24H0z" fill="currentColor"/><path d="M12 18a6 6 0 1 1 0-12 6 6 0 0 1 0 12zm0-2a4 4 0 1 0 0-8 4 4 0 0 0 0 8zM11 1h2v3h-2V1zm0 19h2v3h-2v-3zM3.515 4.929l1.414-1.414L7.05 5.636 5.636 7.05 3.515 4.93zM16.95 18.364l1.414-1.414 2.121 2.121-1.414 1.414-2.121-2.121zm2.121-14.85l1.414 1.415-2.121 2.121-1.414-1.414 2.121-2.121zM5.636 16.95l1.414 1.414-2.121 2.121-1.414-1.414 2.121-2.121zM23 11v2h-3v-2h3zM4 11v2H1v-2h3z"/></symbol>
+</svg>
+<!-- END SVGs -->
 </body>
 </html>

django/contrib/admin/templates/admin/base_site.html

@@ -4,6 +4,9 @@
 
 {% block branding %}
 <h1 id="site-name"><a href="{% url 'admin:index' %}">{{ site_header|default:_('Django administration') }}</a></h1>
+{% if user.is_anonymous %}
+  {% include "admin/color_theme_toggle.html" %}
+{% endif %}
 {% endblock %}
 
 {% block nav-global %}{% endblock %}

django/contrib/admin/templates/admin/color_theme_toggle.html

@@ -0,0 +1,12 @@
+<button class="theme-toggle">
+  <div class="visually-hidden">Toggle Light / Dark / Auto color theme</div>
+  <svg class="theme-icon-when-auto">
+    <use xlink:href="#icon-auto" />
+  </svg>
+  <svg class="theme-icon-when-dark">
+    <use xlink:href="#icon-moon" />
+  </svg>
+  <svg class="theme-icon-when-light">
+    <use xlink:href="#icon-sun" />
+  </svg>
+</button>

django/contrib/admin/templates/registration/password_change_done.html

@@ -6,6 +6,7 @@
     {% csrf_token %}
     <button type="submit">{% translate 'Log out' %}</button>
   </form>
+  {% include "admin/color_theme_toggle.html" %}
 {% endblock %}
 {% block breadcrumbs %}
 <div class="breadcrumbs">

django/contrib/admin/templates/registration/password_change_form.html

@@ -7,6 +7,7 @@
     {% csrf_token %}
     <button type="submit">{% translate 'Log out' %}</button>
   </form>
+  {% include "admin/color_theme_toggle.html" %}
 {% endblock %}
 {% block breadcrumbs %}
 <div class="breadcrumbs">

docs/releases/4.2.txt

@@ -32,7 +32,8 @@ Minor features
 :mod:`django.contrib.admin`
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-* ...
+* The light or dark color theme of the admin can now be toggled in the UI, as
+  well as being set to follow the system setting.
 
 :mod:`django.contrib.admindocs`
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~