diff --git a/allianceauth/custom_css/__init__.py b/allianceauth/custom_css/__init__.py
new file mode 100644
index 00000000..b2dbc39c
--- /dev/null
+++ b/allianceauth/custom_css/__init__.py
@@ -0,0 +1,3 @@
+"""
+Initializes the custom_css module.
+"""
diff --git a/allianceauth/custom_css/admin.py b/allianceauth/custom_css/admin.py
new file mode 100644
index 00000000..093e18e8
--- /dev/null
+++ b/allianceauth/custom_css/admin.py
@@ -0,0 +1,25 @@
+"""
+Admin classes for custom_css app
+"""
+
+# Django
+from django.contrib import admin
+
+# Django Solos
+from solo.admin import SingletonModelAdmin
+
+# Alliance Auth Custom CSS
+from allianceauth.custom_css.models import CustomCSS
+from allianceauth.custom_css.forms import CustomCSSAdminForm
+
+
+@admin.register(CustomCSS)
+class CustomCSSAdmin(SingletonModelAdmin):
+    """
+    Custom CSS Admin
+    """
+
+    form = CustomCSSAdminForm
+
+    # Leave this here for when we decide to add syntax highlighting to the CSS editor
+    # change_form_template = 'custom_css/admin/change_form.html'
diff --git a/allianceauth/custom_css/apps.py b/allianceauth/custom_css/apps.py
new file mode 100644
index 00000000..614f3463
--- /dev/null
+++ b/allianceauth/custom_css/apps.py
@@ -0,0 +1,13 @@
+"""
+Django app configuration for custom_css
+"""
+
+# Django
+from django.apps import AppConfig
+from django.utils.translation import gettext_lazy as _
+
+
+class CustomCSSConfig(AppConfig):
+    name = "allianceauth.custom_css"
+    label = "custom_css"
+    verbose_name = _("Custom CSS")
diff --git a/allianceauth/custom_css/forms.py b/allianceauth/custom_css/forms.py
new file mode 100644
index 00000000..6823b204
--- /dev/null
+++ b/allianceauth/custom_css/forms.py
@@ -0,0 +1,29 @@
+"""
+Forms for custom_css app
+"""
+
+# Alliance Auth Custom CSS
+from allianceauth.custom_css.models import CustomCSS
+from allianceauth.custom_css.widgets import CssEditorWidget
+
+# Django
+from django import forms
+
+
+class CustomCSSAdminForm(forms.ModelForm):
+    """
+    Form for editing custom CSS
+    """
+
+    class Meta:
+        model = CustomCSS
+        fields = ("css",)
+        widgets = {
+            "css": CssEditorWidget(
+                attrs={
+                    "style": "width: 90%; height: 100%;",
+                    "data-editor": "code-highlight",
+                    "data-language": "css",
+                }
+            )
+        }
diff --git a/allianceauth/custom_css/migrations/0001_initial.py b/allianceauth/custom_css/migrations/0001_initial.py
new file mode 100644
index 00000000..8ce51302
--- /dev/null
+++ b/allianceauth/custom_css/migrations/0001_initial.py
@@ -0,0 +1,42 @@
+# Generated by Django 4.2.15 on 2024-08-14 11:25
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    initial = True
+
+    dependencies = []
+
+    operations = [
+        migrations.CreateModel(
+            name="CustomCSS",
+            fields=[
+                (
+                    "id",
+                    models.AutoField(
+                        auto_created=True,
+                        primary_key=True,
+                        serialize=False,
+                        verbose_name="ID",
+                    ),
+                ),
+                (
+                    "css",
+                    models.TextField(
+                        blank=True,
+                        help_text="This CSS will be added to the site after the default CSS.",
+                        null=True,
+                        verbose_name="Your custom CSS",
+                    ),
+                ),
+                ("timestamp", models.DateTimeField(auto_now=True)),
+            ],
+            options={
+                "verbose_name": "Custom CSS",
+                "verbose_name_plural": "Custom CSS",
+                "default_permissions": (),
+            },
+        ),
+    ]
diff --git a/allianceauth/custom_css/migrations/__init__.py b/allianceauth/custom_css/migrations/__init__.py
new file mode 100644
index 00000000..e69de29b
diff --git a/allianceauth/custom_css/models.py b/allianceauth/custom_css/models.py
new file mode 100644
index 00000000..c831cf6b
--- /dev/null
+++ b/allianceauth/custom_css/models.py
@@ -0,0 +1,143 @@
+"""
+Models for the custom_css app
+"""
+
+import os
+import re
+
+# Django Solo
+from solo.models import SingletonModel
+
+# Django
+from django.conf import settings
+from django.db import models
+from django.utils.translation import gettext_lazy as _
+
+
+class CustomCSS(SingletonModel):
+    """
+    Model for storing custom CSS for the site
+    """
+
+    css = models.TextField(
+        blank=True,
+        null=True,
+        verbose_name=_("Your custom CSS"),
+        help_text=_("This CSS will be added to the site after the default CSS."),
+    )
+    timestamp = models.DateTimeField(auto_now=True)
+
+    class Meta:
+        """
+        Meta for CustomCSS
+        """
+
+        default_permissions = ()
+        verbose_name = _("Custom CSS")
+        verbose_name_plural = _("Custom CSS")
+
+    def __str__(self) -> str:
+        """
+        String representation of CustomCSS
+
+        :return:
+        :rtype:
+        """
+
+        return str(_("Custom CSS"))
+
+    def save(self, *args, **kwargs):
+        """
+        Save method for CustomCSS
+
+        :param args:
+        :type args:
+        :param kwargs:
+        :type kwargs:
+        :return:
+        :rtype:
+        """
+
+        self.pk = 1
+
+        if self.css and len(self.css.replace(" ", "")) > 0:
+            # Write the custom CSS to a file
+            custom_css_file = open(
+                f"{settings.STATIC_ROOT}allianceauth/custom-styles.css", "w+"
+            )
+            custom_css_file.write(self.compress_css())
+            custom_css_file.close()
+        else:
+            # Remove the custom CSS file
+            try:
+                os.remove(f"{settings.STATIC_ROOT}allianceauth/custom-styles.css")
+            except FileNotFoundError:
+                pass
+
+        super().save(*args, **kwargs)
+
+    def compress_css(self) -> str:
+        """
+        Compress CSS
+
+        :return:
+        :rtype:
+        """
+
+        css = self.css
+        new_css = ""
+
+        # Remove comments
+        css = re.sub(pattern=r"\s*/\*\s*\*/", repl="$$HACK1$$", string=css)
+        css = re.sub(pattern=r"/\*[\s\S]*?\*/", repl="", string=css)
+        css = css.replace("$$HACK1$$", "/**/")
+
+        # url() doesn't need quotes
+        css = re.sub(pattern=r'url\((["\'])([^)]*)\1\)', repl=r"url(\2)", string=css)
+
+        # Spaces may be safely collapsed as generated content will collapse them anyway.
+        css = re.sub(pattern=r"\s+", repl=" ", string=css)
+
+        # Shorten collapsable colors: #aabbcc to #abc
+        css = re.sub(
+            pattern=r"#([0-9a-f])\1([0-9a-f])\2([0-9a-f])\3(\s|;)",
+            repl=r"#\1\2\3\4",
+            string=css,
+        )
+
+        # Fragment values can loose zeros
+        css = re.sub(
+            pattern=r":\s*0(\.\d+([cm]m|e[mx]|in|p[ctx]))\s*;", repl=r":\1;", string=css
+        )
+
+        for rule in re.findall(pattern=r"([^{]+){([^}]*)}", string=css):
+            # We don't need spaces around operators
+            selectors = [
+                re.sub(
+                    pattern=r"(?<=[\[\(>+=])\s+|\s+(?=[=~^$*|>+\]\)])",
+                    repl=r"",
+                    string=selector.strip(),
+                )
+                for selector in rule[0].split(",")
+            ]
+
+            # Order is important, but we still want to discard repetitions
+            properties = {}
+            porder = []
+
+            for prop in re.findall(pattern="(.*?):(.*?)(;|$)", string=rule[1]):
+                key = prop[0].strip().lower()
+
+                if key not in porder:
+                    porder.append(key)
+
+                properties[key] = prop[1].strip()
+
+            # output rule if it contains any declarations
+            if properties:
+                new_css += "{}{{{}}}".format(
+                    ",".join(selectors),
+                    "".join([f"{key}:{properties[key]};" for key in porder])[:-1],
+                )
+
+        return new_css
diff --git a/allianceauth/custom_css/templates/custom_css/admin/change_form.html b/allianceauth/custom_css/templates/custom_css/admin/change_form.html
new file mode 100644
index 00000000..d8c921f2
--- /dev/null
+++ b/allianceauth/custom_css/templates/custom_css/admin/change_form.html
@@ -0,0 +1,48 @@
+{% extends "admin/change_form.html" %}
+
+{% block field_sets %}
+    {% for fieldset in adminform %}
+        <fieldset class="module aligned {{ fieldset.classes }}">
+            {% if fieldset.name %}<h2>{{ fieldset.name }}</h2>{% endif %}
+
+            {% if fieldset.description %}
+                <div class="description">{{ fieldset.description|safe }}</div>
+            {% endif %}
+
+            {% for line in fieldset %}
+                <div class="form-row{% if line.fields|length == 1 and line.errors %} errors{% endif %}{% if not line.has_visible_field %} hidden{% endif %}{% for field in line %}{% if field.field.name %} field-{{ field.field.name }}{% endif %}{% endfor %}">
+                    {% if line.fields|length == 1 %}{{ line.errors }}{% else %}<div class="flex-container form-multiline">{% endif %}
+
+                    {% for field in line %}
+                        <div>
+                            {% if not line.fields|length == 1 and not field.is_readonly %}{{ field.errors }}{% endif %}
+
+                            <div class="flex-container{% if not line.fields|length == 1 %} fieldBox{% if field.field.name %} field-{{ field.field.name }}{% endif %}{% if not field.is_readonly and field.errors %} errors{% endif %}{% if field.field.is_hidden %} hidden{% endif %}{% elif field.is_checkbox %} checkbox-row{% endif %}">
+                                {% if field.is_checkbox %}
+                                    {{ field.field }}{{ field.label_tag }}
+                                {% else %}
+                                    {{ field.label_tag }}
+                                    {% if field.is_readonly %}
+                                        <div class="readonly">{{ field.contents }}</div>
+                                    {% else %}
+                                        {{ field.field }}
+                                    {% endif %}
+                                {% endif %}
+                            </div>
+
+                            {% if field.field.help_text %}
+                                <div class="help"{% if field.field.id_for_label %} id="{{ field.field.id_for_label }}_helptext"{% endif %}>
+                                    <div>{{ field.field.help_text|safe }}</div>
+                                </div>
+                            {% endif %}
+                        </div>
+                    {% endfor %}
+
+                    {% if not line.fields|length == 1 %}</div>{% endif %}
+                </div>
+            {% endfor %}
+        </fieldset>
+    {% endfor %}
+{% endblock %}
+
+{% block after_field_sets %}{% endblock %}
diff --git a/allianceauth/custom_css/templates/custom_css/bundles/custom-css.html b/allianceauth/custom_css/templates/custom_css/bundles/custom-css.html
new file mode 100644
index 00000000..4dd634ed
--- /dev/null
+++ b/allianceauth/custom_css/templates/custom_css/bundles/custom-css.html
@@ -0,0 +1,3 @@
+{% load custom_css %}
+
+{% custom_css_static 'allianceauth/custom-styles.css' %}
diff --git a/allianceauth/custom_css/templatetags/__init__.py b/allianceauth/custom_css/templatetags/__init__.py
new file mode 100644
index 00000000..e0365e18
--- /dev/null
+++ b/allianceauth/custom_css/templatetags/__init__.py
@@ -0,0 +1,3 @@
+"""
+Init file for custom_css templatetags
+"""
diff --git a/allianceauth/custom_css/templatetags/custom_css.py b/allianceauth/custom_css/templatetags/custom_css.py
new file mode 100644
index 00000000..3c01602f
--- /dev/null
+++ b/allianceauth/custom_css/templatetags/custom_css.py
@@ -0,0 +1,48 @@
+"""
+Custom template tags for custom_css app
+"""
+
+# Alliance Auth Custom CSS
+from allianceauth.custom_css.models import CustomCSS
+
+# Django
+from django.conf import settings
+from django.template.defaulttags import register
+from django.templatetags.static import static
+from django.utils.safestring import mark_safe
+
+from pathlib import Path
+
+
+@register.simple_tag
+def custom_css_static(path: str) -> str:
+    """
+    Versioned static URL
+    This is to make sure to break the browser cache on CSS updates.
+
+    Example: /static/allianceauth/custom-styles.css?v=1234567890
+
+    :param path:
+    :type path:
+    :return:
+    :rtype:
+    """
+
+    try:
+        Path(f"{settings.STATIC_ROOT}{path}").resolve(strict=True)
+    except FileNotFoundError:
+        return ""
+    else:
+        try:
+            custom_css = CustomCSS.objects.get(pk=1)
+        except CustomCSS.DoesNotExist:
+            return ""
+        else:
+            custom_css_changed = custom_css.timestamp.timestamp()
+            custom_css_version = (
+                str(custom_css_changed).replace(" ", "").replace(":", "").replace("-", "")
+            )  # remove spaces, colons, and dashes
+            static_url = static(path)
+            versioned_url = static_url + "?v=" + custom_css_version
+
+            return mark_safe(f'<link rel="stylesheet" href="{versioned_url}">')
diff --git a/allianceauth/custom_css/widgets.py b/allianceauth/custom_css/widgets.py
new file mode 100644
index 00000000..32ed07dd
--- /dev/null
+++ b/allianceauth/custom_css/widgets.py
@@ -0,0 +1,38 @@
+"""
+Form widgets for custom_css app
+"""
+
+# Django
+from django import forms
+
+# Alliance Auth
+from allianceauth.custom_css.models import CustomCSS
+
+
+class CssEditorWidget(forms.Textarea):
+    """
+    Widget for editing CSS
+    """
+
+    def __init__(self, attrs=None):
+        default_attrs = {"class": "custom-css-editor"}
+
+        if attrs:
+            default_attrs.update(attrs)
+
+        super().__init__(default_attrs)
+
+    # For when we want to add some sort of syntax highlight to it, which is not that
+    # easy to do on a textarea field though.
+    # `highlight.js` is just used as an example here, and doesn't work on a textarea field.
+    # class Media:
+    #     css = {
+    #         "all": (
+    #             "/static/custom_css/libs/highlight.js/11.10.0/styles/github.min.css",
+    #         )
+    #     }
+    #     js = (
+    #         "/static/custom_css/libs/highlight.js/11.10.0/highlight.min.js",
+    #         "/static/custom_css/libs/highlight.js/11.10.0/languages/css.min.js",
+    #         "/static/custom_css/javascript/custom-css.min.js",
+    #     )
diff --git a/allianceauth/project_template/project_name/settings/base.py b/allianceauth/project_template/project_name/settings/base.py
index 0291913b..cf26fe4a 100644
--- a/allianceauth/project_template/project_name/settings/base.py
+++ b/allianceauth/project_template/project_name/settings/base.py
@@ -22,6 +22,7 @@ INSTALLED_APPS = [
     'django.contrib.staticfiles',
     'django.contrib.humanize',
     'django_celery_beat',
+    'solo',
     'bootstrapform',
     'django_bootstrap5',  # https://github.com/zostera/django-bootstrap5
     'sortedm2m',
@@ -39,6 +40,7 @@ INSTALLED_APPS = [
     'allianceauth.theme.darkly',
     'allianceauth.theme.flatly',
     'allianceauth.theme.materia',
+    "allianceauth.custom_css",
 ]
 
 SECRET_KEY = "wow I'm a really bad default secret key"
diff --git a/allianceauth/templates/allianceauth/base-bs5.html b/allianceauth/templates/allianceauth/base-bs5.html
index 58235b9e..4e9a31eb 100644
--- a/allianceauth/templates/allianceauth/base-bs5.html
+++ b/allianceauth/templates/allianceauth/base-bs5.html
@@ -35,6 +35,8 @@
         </style>
 
         {% block extra_css %}{% endblock extra_css %}
+
+        {% include 'custom_css/bundles/custom-css.html' %}
     </head>
 
     <body>
diff --git a/pyproject.toml b/pyproject.toml
index a2568a40..35edbe64 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -50,6 +50,7 @@ dependencies = [
     "django-esi>=5",
     "django-redis>=5.2",
     "django-registration<3.4,>=3.3",
+    "django-solo",
     "django-sortedm2m",
     "dnspython",
     "mysqlclient>=2.1",