diff --git a/qutebrowser/config/configdata.py b/qutebrowser/config/configdata.py
index 080fd59a8..ca7a846c7 100644
--- a/qutebrowser/config/configdata.py
+++ b/qutebrowser/config/configdata.py
@@ -268,7 +268,7 @@ DATA = collections.OrderedDict([
          "This will flatten all the frames to become one scrollable page."),
 
         ('user-stylesheet',
-         SettingValue(typ.WebSettingsFile(), ''),
+         SettingValue(typ.UserStyleSheet(), ''),
          "User stylesheet to use."),
 
         ('css-media-type',
diff --git a/qutebrowser/config/configtypes.py b/qutebrowser/config/configtypes.py
index c50094a93..a8178c164 100644
--- a/qutebrowser/config/configtypes.py
+++ b/qutebrowser/config/configtypes.py
@@ -21,6 +21,7 @@
 
 import re
 import shlex
+import base64
 import codecs
 import os.path
 import sre_constants
@@ -1082,20 +1083,43 @@ class Encoding(BaseType):
             raise ValidationError(value, "is not a valid encoding!")
 
 
-class WebSettingsFile(File):
+class UserStyleSheet(File):
 
-    """QWebSettings file."""
+    """QWebSettings UserStyleSheet."""
 
-    typestr = 'file'
+    typestr = 'user-stylesheet'
 
     def __init__(self):
         super().__init__(none_ok=True)
 
+    def validate(self, value):
+        if not value:
+            if self.none_ok:
+                return
+            else:
+                raise ValidationError(value, "may not be empty!")
+        value = os.path.expanduser(value)
+        if not os.path.isabs(value):
+            # probably a CSS, so we don't handle it as filename.
+            # FIXME We just try if it is encodable, maybe we should validate
+            # CSS?
+            try:
+                value.encode('utf-8')
+            except UnicodeEncodeError as e:
+                raise ValidationError(value, str(e))
+            return
+        elif not os.path.isfile(value):
+            raise ValidationError(value, "must be a valid file!")
+
     def transform(self, value):
+        path = os.path.expanduser(value)
         if not value:
             return None
+        elif os.path.isabs(path):
+            return QUrl.fromLocalFile(path)
         else:
-            return QUrl.fromLocalFile(value)
+            data = base64.b64encode(value.encode('utf-8')).decode('ascii')
+            return QUrl("data:text/css;charset=utf-8;base64,{}".format(data))
 
 
 class AutoSearch(BaseType):
diff --git a/qutebrowser/test/config/test_configtypes.py b/qutebrowser/test/config/test_configtypes.py
index aa17c9436..59d654be2 100644
--- a/qutebrowser/test/config/test_configtypes.py
+++ b/qutebrowser/test/config/test_configtypes.py
@@ -21,6 +21,8 @@
 import unittest
 import re
 import collections
+import os.path
+import base64
 from unittest import mock
 
 from qutebrowser.config import configtypes
@@ -1759,20 +1761,27 @@ class KeyBindingNameTests(unittest.TestCase):
         self.assertEqual(self.t.transform("foobar"), "foobar")
 
 
-class WebSettingsFileTests(unittest.TestCase):
+class UserStyleSheetTests(unittest.TestCase):
 
-    """Test WebSettingsFile."""
+    """Test UserStyleSheet."""
 
     def setUp(self):
-        self.t = configtypes.WebSettingsFile()
+        self.t = configtypes.UserStyleSheet()
 
     def test_transform_empty(self):
         """Test transform with an empty value."""
         self.assertIsNone(self.t.transform(''))
 
-    def test_transform(self):
-        """Test transform with a value."""
-        self.assertEqual(self.t.transform("/foo/bar"), QUrl("file:///foo/bar"))
+    def test_transform_file(self):
+        """Test transform with a filename."""
+        path = os.path.join(os.path.sep, 'foo', 'bar')
+        self.assertEqual(self.t.transform(path), QUrl("file:///foo/bar"))
+
+    def test_transform_base64(self):
+        """Test transform with a data string."""
+        b64 = base64.b64encode(b"test").decode('ascii')
+        url = QUrl("data:text/css;charset=utf-8;base64,{}".format(b64))
+        self.assertEqual(self.t.transform("test"), url)
 
 
 class AutoSearchTests(unittest.TestCase):