diff --git a/core/lib/Drupal/Core/Asset/CssOptimizer.php b/core/lib/Drupal/Core/Asset/CssOptimizer.php
index 94c2240abc..769e81e384 100644
--- a/core/lib/Drupal/Core/Asset/CssOptimizer.php
+++ b/core/lib/Drupal/Core/Asset/CssOptimizer.php
@@ -60,8 +60,9 @@ protected function processFile($css_asset) {
     // 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', [$this, 'rewriteFileURI'], $contents);
+    // Anchor all paths in the CSS with its base URL, ignoring external and
+    // absolute paths or svg selectors (starting with # or %23).
+    return preg_replace_callback('/url\(\s*[\'"]?(?![a-z]+:|\/+|\#|\%23+)([^\'")]+)[\'"]?\s*\)/i', [$this, 'rewriteFileURI'], $contents);
   }
 
   /**
@@ -167,7 +168,7 @@ protected function loadNestedFile($matches) {
 
     // Alter all internal url() paths. Leave external paths alone. We don't need
     // to normalize absolute paths here because that will be done later.
-    return preg_replace('/url\(\s*([\'"]?)(?![a-z]+:|\/+)([^\'")]+)([\'"]?)\s*\)/i', 'url(\1' . $directory . '\2\3)', $file);
+    return preg_replace('/url\(\s*([\'"]?)(?![a-z]+:|\/+|\#|\%23+)([^\'")]+)([\'"]?)\s*\)/i', 'url(\1' . $directory . '\2\3)', $file);
   }
 
   /**
diff --git a/core/tests/Drupal/Tests/Core/Asset/css_test_files/css_input_with_import.css.optimized.css b/core/tests/Drupal/Tests/Core/Asset/css_test_files/css_input_with_import.css.optimized.css
index 16bd93be7e..f905e91fa2 100644
--- a/core/tests/Drupal/Tests/Core/Asset/css_test_files/css_input_with_import.css.optimized.css
+++ b/core/tests/Drupal/Tests/Core/Asset/css_test_files/css_input_with_import.css.optimized.css
@@ -1,4 +1,4 @@
-ul,select{font:1em/160% Verdana,sans-serif;color:#494949;}.ui-icon{background-image:url(images/icon.png);}.data .double-quote{background-image:url("data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7");}.data .single-quote{background-image:url('data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD/2wBDACAWGBwYFCAcGhwkIiAmMFA0MCwsMGJGSjpQdGZ6eHJmcG6AkLicgIiuim5woNqirr7EztDOfJri8uDI8LjKzsb/2wBDASIkJDAqMF40NF7GhHCExsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsb/wAARCAABAAEDASIAAhEBAxEB/8QAFQABAQAAAAAAAAAAAAAAAAAAAAb/xAAUEAEAAAAAAAAAAAAAAAAAAAAA/8QAFAEBAAAAAAAAAAAAAAAAAAAAAP/EABQRAQAAAAAAAAAAAAAAAAAAAAD/2gAMAwEAAhEDEQA/AKAAH//Z');}.data .no-quote{background-image:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACEAAAAEAQAAAAAo/mtHAAAAIElEQVQIHWMRnWHwcRNLN8NZ7QYWwT8PlBlYsgqVBRsAankIMw5MtnoAAAAASUVORK5CYII=);}
+ul,select{font:1em/160% Verdana,sans-serif;color:#494949;}.ui-icon{background-image:url(images/icon.png);}.data .double-quote{background-image:url("data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7");}.data .single-quote{background-image:url('data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD/2wBDACAWGBwYFCAcGhwkIiAmMFA0MCwsMGJGSjpQdGZ6eHJmcG6AkLicgIiuim5woNqirr7EztDOfJri8uDI8LjKzsb/2wBDASIkJDAqMF40NF7GhHCExsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsb/wAARCAABAAEDASIAAhEBAxEB/8QAFQABAQAAAAAAAAAAAAAAAAAAAAb/xAAUEAEAAAAAAAAAAAAAAAAAAAAA/8QAFAEBAAAAAAAAAAAAAAAAAAAAAP/EABQRAQAAAAAAAAAAAAAAAAAAAAD/2gAMAwEAAhEDEQA/AKAAH//Z');}.data .no-quote{background-image:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACEAAAAEAQAAAAAo/mtHAAAAIElEQVQIHWMRnWHwcRNLN8NZ7QYWwT8PlBlYsgqVBRsAankIMw5MtnoAAAAASUVORK5CYII=);}.svg-clip{clip-path:url('#svg');}
 p,select{font:1em/160% Verdana,sans-serif;color:#494949;}
 @import url("http://example.com/style.css");@import url("//example.com/style.css");body{margin:0;padding:0;background:#edf5fa;font:76%/170% Verdana,sans-serif;color:#494949;}.this .is .a .test{font:1em/100% Verdana,sans-serif;color:#494949;}.this
 .is
diff --git a/core/tests/Drupal/Tests/Core/Asset/css_test_files/css_subfolder/css_input_with_import.css.optimized.css b/core/tests/Drupal/Tests/Core/Asset/css_test_files/css_subfolder/css_input_with_import.css.optimized.css
index 816039dc92..db8a13458e 100644
--- a/core/tests/Drupal/Tests/Core/Asset/css_test_files/css_subfolder/css_input_with_import.css.optimized.css
+++ b/core/tests/Drupal/Tests/Core/Asset/css_test_files/css_subfolder/css_input_with_import.css.optimized.css
@@ -1,4 +1,4 @@
-ul,select{font:1em/160% Verdana,sans-serif;color:#494949;}.ui-icon{background-image:url(../images/icon.png);}.data .double-quote{background-image:url("data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7");}.data .single-quote{background-image:url('data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD/2wBDACAWGBwYFCAcGhwkIiAmMFA0MCwsMGJGSjpQdGZ6eHJmcG6AkLicgIiuim5woNqirr7EztDOfJri8uDI8LjKzsb/2wBDASIkJDAqMF40NF7GhHCExsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsb/wAARCAABAAEDASIAAhEBAxEB/8QAFQABAQAAAAAAAAAAAAAAAAAAAAb/xAAUEAEAAAAAAAAAAAAAAAAAAAAA/8QAFAEBAAAAAAAAAAAAAAAAAAAAAP/EABQRAQAAAAAAAAAAAAAAAAAAAAD/2gAMAwEAAhEDEQA/AKAAH//Z');}.data .no-quote{background-image:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACEAAAAEAQAAAAAo/mtHAAAAIElEQVQIHWMRnWHwcRNLN8NZ7QYWwT8PlBlYsgqVBRsAankIMw5MtnoAAAAASUVORK5CYII=);}
+ul,select{font:1em/160% Verdana,sans-serif;color:#494949;}.ui-icon{background-image:url(../images/icon.png);}.data .double-quote{background-image:url("data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7");}.data .single-quote{background-image:url('data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD/2wBDACAWGBwYFCAcGhwkIiAmMFA0MCwsMGJGSjpQdGZ6eHJmcG6AkLicgIiuim5woNqirr7EztDOfJri8uDI8LjKzsb/2wBDASIkJDAqMF40NF7GhHCExsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsbGxsb/wAARCAABAAEDASIAAhEBAxEB/8QAFQABAQAAAAAAAAAAAAAAAAAAAAb/xAAUEAEAAAAAAAAAAAAAAAAAAAAA/8QAFAEBAAAAAAAAAAAAAAAAAAAAAP/EABQRAQAAAAAAAAAAAAAAAAAAAAD/2gAMAwEAAhEDEQA/AKAAH//Z');}.data .no-quote{background-image:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACEAAAAEAQAAAAAo/mtHAAAAIElEQVQIHWMRnWHwcRNLN8NZ7QYWwT8PlBlYsgqVBRsAankIMw5MtnoAAAAASUVORK5CYII=);}.svg-clip{clip-path:url('#svg');}
 p,select{font:1em/160% Verdana,sans-serif;color:#494949;}
 body{margin:0;padding:0;background:#edf5fa;font:76%/170% Verdana,sans-serif;color:#494949;}.this .is .a .test{font:1em/100% Verdana,sans-serif;color:#494949;}.this
 .is
diff --git a/core/tests/Drupal/Tests/Core/Asset/css_test_files/import1.css b/core/tests/Drupal/Tests/Core/Asset/css_test_files/import1.css
index e53d6d52cd..a1e38a08c7 100644
--- a/core/tests/Drupal/Tests/Core/Asset/css_test_files/import1.css
+++ b/core/tests/Drupal/Tests/Core/Asset/css_test_files/import1.css
@@ -18,3 +18,8 @@ ul, select {
 .data .no-quote {
   background-image: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACEAAAAEAQAAAAAo/mtHAAAAIElEQVQIHWMRnWHwcRNLN8NZ7QYWwT8PlBlYsgqVBRsAankIMw5MtnoAAAAASUVORK5CYII=);
 }
+
+/* Test SVG hash url */
+.svg-clip {
+  clip-path: url('#svg');
+}