diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 2aef832c..a9e9441 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -330,10 +330,10 @@ function theme_get_setting($setting_name, $theme = NULL) {
       if ($cache[$theme]->get('features.logo')) {
         $logo_path = $cache[$theme]->get('logo.path');
         if ($cache[$theme]->get('logo.use_default')) {
-          $cache[$theme]->set('logo.url', file_create_url($theme_object->getPath() . '/logo.svg'));
+          $cache[$theme]->set('logo.url', file_url_transform_relative(file_create_url($theme_object->getPath() . '/logo.svg')));
         }
         elseif ($logo_path) {
-          $cache[$theme]->set('logo.url', file_create_url($logo_path));
+          $cache[$theme]->set('logo.url', file_url_transform_relative(file_create_url($logo_path)));
         }
       }
 
@@ -342,14 +342,14 @@ function theme_get_setting($setting_name, $theme = NULL) {
         $favicon_path = $cache[$theme]->get('favicon.path');
         if ($cache[$theme]->get('favicon.use_default')) {
           if (file_exists($favicon = $theme_object->getPath() . '/favicon.ico')) {
-            $cache[$theme]->set('favicon.url', file_create_url($favicon));
+            $cache[$theme]->set('favicon.url', file_url_transform_relative(file_create_url($favicon)));
           }
           else {
-            $cache[$theme]->set('favicon.url', file_create_url('core/misc/favicon.ico'));
+            $cache[$theme]->set('favicon.url', file_url_transform_relative(file_create_url('core/misc/favicon.ico')));
           }
         }
         elseif ($favicon_path) {
-          $cache[$theme]->set('favicon.url', file_create_url($favicon_path));
+          $cache[$theme]->set('favicon.url', file_url_transform_relative(file_create_url($favicon_path)));
         }
         else {
           $cache[$theme]->set('features.favicon', FALSE);
diff --git a/core/lib/Drupal/Core/Asset/CssCollectionRenderer.php b/core/lib/Drupal/Core/Asset/CssCollectionRenderer.php
index eeed904..3b192b4 100644
--- a/core/lib/Drupal/Core/Asset/CssCollectionRenderer.php
+++ b/core/lib/Drupal/Core/Asset/CssCollectionRenderer.php
@@ -134,7 +134,7 @@ public function render(array $css_assets) {
           // assets: output a LINK tag for a file CSS asset.
           if (count($css_assets) <= 31) {
             $element = $link_element_defaults;
-            $element['#attributes']['href'] = file_create_url($css_asset['data']) . $query_string_separator . $query_string;
+            $element['#attributes']['href'] = file_url_transform_relative(file_create_url($css_asset['data'])) . $query_string_separator . $query_string;
             $element['#attributes']['media'] = $css_asset['media'];
             $element['#browsers'] = $css_asset['browsers'];
             $elements[] = $element;
@@ -167,7 +167,7 @@ public function render(array $css_assets) {
                 // control browser-caching. IE7 does not support a media type on
                 // the @import statement, so we instead specify the media for
                 // the group on the STYLE tag.
-                $import[] = '@import url("' . SafeMarkup::checkPlain(file_create_url($next_css_asset['data']) . '?' . $query_string) . '");';
+                $import[] = '@import url("' . SafeMarkup::checkPlain(file_url_transform_relative(file_create_url($next_css_asset['data'])) . '?' . $query_string) . '");';
                 // Move the outer for loop skip the next item, since we
                 // processed it here.
                 $i = $j;
diff --git a/core/lib/Drupal/Core/Asset/CssOptimizer.php b/core/lib/Drupal/Core/Asset/CssOptimizer.php
index b93a638..c199e08 100644
--- a/core/lib/Drupal/Core/Asset/CssOptimizer.php
+++ b/core/lib/Drupal/Core/Asset/CssOptimizer.php
@@ -233,7 +233,7 @@ public function rewriteFileURI($matches) {
       $last = $path;
       $path = preg_replace('`(^|/)(?!\.\./)([^/]+)/\.\./`', '$1', $path);
     }
-    return 'url(' . file_create_url($path) . ')';
+    return 'url(' . file_url_transform_relative(file_create_url($path)) . ')';
   }
 
 }
diff --git a/core/lib/Drupal/Core/Asset/JsCollectionRenderer.php b/core/lib/Drupal/Core/Asset/JsCollectionRenderer.php
index 7db84ab..e40d0f0 100644
--- a/core/lib/Drupal/Core/Asset/JsCollectionRenderer.php
+++ b/core/lib/Drupal/Core/Asset/JsCollectionRenderer.php
@@ -80,7 +80,7 @@ public function render(array $js_assets) {
         case 'file':
           $query_string = $js_asset['version'] == -1 ? $default_query_string : 'v=' . $js_asset['version'];
           $query_string_separator = (strpos($js_asset['data'], '?') !== FALSE) ? '&' : '?';
-          $element['#attributes']['src'] = file_create_url($js_asset['data']);
+          $element['#attributes']['src'] = file_url_transform_relative(file_create_url($js_asset['data']));
           // Only add the cache-busting query string if this isn't an aggregate
           // file.
           if (!isset($js_asset['preprocessed'])) {
diff --git a/core/modules/color/src/Tests/ColorTest.php b/core/modules/color/src/Tests/ColorTest.php
index 3456dca..1c4f41d 100644
--- a/core/modules/color/src/Tests/ColorTest.php
+++ b/core/modules/color/src/Tests/ColorTest.php
@@ -121,7 +121,7 @@ function _testColor($theme, $test_values) {
     $this->drupalGet('<front>');
     $stylesheets = $this->config('color.theme.' . $theme)->get('stylesheets');
     foreach ($stylesheets as $stylesheet) {
-      $this->assertPattern('|' . file_create_url($stylesheet) . '|', 'Make sure the color stylesheet is included in the content. (' . $theme . ')');
+      $this->assertPattern('|' . file_url_transform_relative(file_create_url($stylesheet)) . '|', 'Make sure the color stylesheet is included in the content. (' . $theme . ')');
       $stylesheet_content = join("\n", file($stylesheet));
       $this->assertTrue(strpos($stylesheet_content, 'color: #123456') !== FALSE, 'Make sure the color we changed is in the color stylesheet. (' . $theme . ')');
     }
diff --git a/core/modules/system/src/Tests/System/ThemeTest.php b/core/modules/system/src/Tests/System/ThemeTest.php
index d5bb6f6..d8e75c7 100644
--- a/core/modules/system/src/Tests/System/ThemeTest.php
+++ b/core/modules/system/src/Tests/System/ThemeTest.php
@@ -61,27 +61,27 @@ function testThemeSettings() {
       // Raw stream wrapper URI.
       $file->uri => array(
         'form' => file_uri_target($file->uri),
-        'src' => file_create_url($file->uri),
+        'src' => file_url_transform_relative(file_create_url($file->uri)),
       ),
       // Relative path within the public filesystem.
       file_uri_target($file->uri) => array(
         'form' => file_uri_target($file->uri),
-        'src' => file_create_url($file->uri),
+        'src' => file_url_transform_relative(file_create_url($file->uri)),
       ),
       // Relative path to a public file.
       $file_relative => array(
         'form' => $file_relative,
-        'src' => file_create_url($file->uri),
+        'src' => file_url_transform_relative(file_create_url($file->uri)),
       ),
       // Relative path to an arbitrary file.
       'core/misc/druplicon.png' => array(
         'form' => 'core/misc/druplicon.png',
-        'src' => $GLOBALS['base_url'] . '/' . 'core/misc/druplicon.png',
+        'src' => base_path() . 'core/misc/druplicon.png',
       ),
       // Relative path to a file in a theme.
       $default_theme_path . '/logo.svg' => array(
         'form' => $default_theme_path . '/logo.svg',
-        'src' => $GLOBALS['base_url'] . '/' . $default_theme_path . '/logo.svg',
+        'src' => base_path() . $default_theme_path . '/logo.svg',
       ),
     );
     foreach ($supported_paths as $input => $expected) {
@@ -179,7 +179,7 @@ function testThemeSettings() {
         ':rel' => 'home',
       )
     );
-    $this->assertEqual($elements[0]['src'], file_create_url($uploaded_filename));
+    $this->assertEqual($elements[0]['src'], file_url_transform_relative(file_create_url($uploaded_filename)));
   }
 
   /**
diff --git a/core/tests/Drupal/Tests/Core/Asset/CssCollectionRendererUnitTest.php b/core/tests/Drupal/Tests/Core/Asset/CssCollectionRendererUnitTest.php
index ad3c80f..73b1f11 100644
--- a/core/tests/Drupal/Tests/Core/Asset/CssCollectionRendererUnitTest.php
+++ b/core/tests/Drupal/Tests/Core/Asset/CssCollectionRendererUnitTest.php
@@ -22,13 +22,16 @@
   function file_create_url($uri) {
     return 'file_create_url:' . $uri;
   }
-
 }
-
+if (!function_exists('file_url_transform_relative')) {
+  /**
+   * Temporary mock of file_url_transform_relative.
+   */
+  function file_url_transform_relative($uri) {
+    return $uri;
+  }
+}
 }
-
-
-
 
 namespace Drupal\Tests\Core\Asset {
 
diff --git a/core/tests/Drupal/Tests/Core/Asset/CssOptimizerUnitTest.php b/core/tests/Drupal/Tests/Core/Asset/CssOptimizerUnitTest.php
index f4d083c..252694e 100644
--- a/core/tests/Drupal/Tests/Core/Asset/CssOptimizerUnitTest.php
+++ b/core/tests/Drupal/Tests/Core/Asset/CssOptimizerUnitTest.php
@@ -32,6 +32,14 @@ function file_uri_scheme($uri) {
   }
 
 }
+if (!function_exists('file_url_transform_relative')) {
+  /**
+   * Temporary mock of file_url_transform_relative.
+   */
+  function file_url_transform_relative($uri) {
+    return $uri;
+  }
+}
 
 }