core/includes/file.inc                                             | 2 +-
 core/lib/Drupal/Core/Asset/CssOptimizer.php                        | 7 ++-----
 .../Drupal/Tests/Core/Asset/CssCollectionRendererUnitTest.php      | 2 +-
 core/tests/Drupal/Tests/Core/Asset/CssOptimizerUnitTest.php        | 2 +-
 4 files changed, 5 insertions(+), 8 deletions(-)

diff --git a/core/includes/file.inc b/core/includes/file.inc
index 3e5eb8c..41d01dd 100644
--- a/core/includes/file.inc
+++ b/core/includes/file.inc
@@ -216,7 +216,7 @@ function file_create_url($uri) {
       // If this is not a properly formatted stream, then it is a shipped file.
       // Therefore, return the urlencoded URI with the base URL prepended.
       $options = UrlHelper::parse($uri);
-      $path = $GLOBALS['base_url'] . '/' . UrlHelper::encodePath($options['path']);
+      $path = $GLOBALS['base_path'] . UrlHelper::encodePath($options['path']);
       // Append the query.
       if ($options['query']) {
         $path .= '?' . UrlHelper::buildQuery($options['query']);
diff --git a/core/lib/Drupal/Core/Asset/CssOptimizer.php b/core/lib/Drupal/Core/Asset/CssOptimizer.php
index d048a3e..dc34a23 100644
--- a/core/lib/Drupal/Core/Asset/CssOptimizer.php
+++ b/core/lib/Drupal/Core/Asset/CssOptimizer.php
@@ -61,17 +61,14 @@ public function clean($contents) {
    * Build aggregate CSS file.
    */
   protected function processFile($css_asset) {
-    global $base_path;
-
     $contents = $this->loadFile($css_asset['data'], TRUE);
 
     $contents = $this->clean($contents);
 
     // Get the parent directory of this file, relative to the Drupal root.
     $css_base_path = substr($css_asset['data'], 0, strrpos($css_asset['data'], '/'));
-    // Store base path. Ensure it is a prefix that will result in root-relative
-    // file URLs.
-    $this->rewriteFileURIBasePath = $base_path . $css_base_path . '/';
+    // Store base path.
+    $this->rewriteFileURIBasePath = $css_base_path . '/';
 
     // Anchor all paths in the CSS with its base URL, ignoring external and absolute paths.
     return preg_replace_callback('/url\(\s*[\'"]?(?![a-z]+:|\/+)([^\'")]+)[\'"]?\s*\)/i', array($this, 'rewriteFileURI'), $contents);
diff --git a/core/tests/Drupal/Tests/Core/Asset/CssCollectionRendererUnitTest.php b/core/tests/Drupal/Tests/Core/Asset/CssCollectionRendererUnitTest.php
index eab4fe4..96f5424 100644
--- a/core/tests/Drupal/Tests/Core/Asset/CssCollectionRendererUnitTest.php
+++ b/core/tests/Drupal/Tests/Core/Asset/CssCollectionRendererUnitTest.php
@@ -20,7 +20,7 @@
    * Component/Utility.
    */
   function file_create_url($uri) {
-    return 'file_create_url:' . $uri;
+    return 'file_create_url:/' . $uri;
   }
 
 }
diff --git a/core/tests/Drupal/Tests/Core/Asset/CssOptimizerUnitTest.php b/core/tests/Drupal/Tests/Core/Asset/CssOptimizerUnitTest.php
index f9a9383..c9b3138 100644
--- a/core/tests/Drupal/Tests/Core/Asset/CssOptimizerUnitTest.php
+++ b/core/tests/Drupal/Tests/Core/Asset/CssOptimizerUnitTest.php
@@ -20,7 +20,7 @@
    * Component/Utility.
    */
   function file_create_url($uri) {
-    return 'file_create_url:' . $uri;
+    return 'file_create_url:/' . $uri;
   }
 
 }