diff --git a/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php b/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php
index 03b458f5e5..b3f0f3dce4 100644
--- a/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php
+++ b/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php
@@ -39,6 +39,26 @@ class LibraryDiscoveryParser {
    */
   protected $root;
 
+  /**
+   * The list of asset paths / sources that have libraries-override applied.
+   *
+   * @var array
+   */
+  protected $overriddenLibraryPaths = [];
+
+  /**
+   * Used to retrieve original libraries-override keys from base theme paths.
+   *
+   * This is used to maintain backward compatibility with previous
+   * libraries-override behavior where overriding of already overridden paths
+   * required using the full Drupal-root-relative path of the last override.
+   *
+   * @todo Remove BC layer in Drupal 9.0.0 https://www.drupal.org/node/2852314.
+   *
+   * @var array
+   */
+  protected $originalLibraryPaths = [];
+
   /**
    * The stream wrapper manager.
    *
@@ -160,6 +180,14 @@ public function buildByExtension($extension) {
         }
         foreach ($library[$type] as $source => $options) {
           unset($library[$type][$source]);
+          // Get the actual overridden path to $source in libraries-override.
+          $source = $this->getLatestOverridePath($source, $type, $id, $extension);
+          if (!$source) {
+            // If $source is false, it means that a libraries-override entry in
+            // the theme or base theme has specified that the library should be
+            // removed. Hence this entry should not be processed.
+            continue;
+          }
           // Allow to omit the options hashmap in YAML declarations.
           if (!is_array($options)) {
             $options = [];
@@ -352,8 +380,8 @@ protected function applyLibrariesOverride($libraries, $extension) {
     // ActiveTheme::getLibrariesOverride() returns libraries-overrides for the
     // current theme as well as all its base themes.
     $all_libraries_overrides = $active_theme->getLibrariesOverride();
-    foreach ($all_libraries_overrides as $theme_path => $libraries_overrides) {
-      foreach ($libraries as $library_name => $library) {
+    foreach ($libraries as $library_name => $library) {
+      foreach ($all_libraries_overrides as $theme_path => $libraries_overrides) {
         // Process libraries overrides.
         if (isset($libraries_overrides["$extension/$library_name"])) {
           // Active theme defines an override for this library.
@@ -373,23 +401,23 @@ protected function applyLibrariesOverride($libraries, $extension) {
           elseif (is_array($override_definition)) {
             // An array definition implies an override for an asset within this
             // library.
-            foreach ($override_definition as $sub_key => $value) {
+            foreach ($override_definition as $type => $value) {
               // Throw an exception if the asset is not properly specified.
               if (!is_array($value)) {
-                throw new InvalidLibrariesOverrideSpecificationException(sprintf('Library asset %s is not correctly specified. It should be in the form "extension/library_name/sub_key/path/to/asset.js".', "$extension/$library_name/$sub_key"));
+                throw new InvalidLibrariesOverrideSpecificationException(sprintf('Library asset %s is not correctly specified. It should be in the form "extension/library_name/sub_key/path/to/asset.js".', "$extension/$library_name/$type"));
               }
-              if ($sub_key === 'drupalSettings') {
+              if ($type === 'drupalSettings') {
                 // drupalSettings may not be overridden.
-                throw new InvalidLibrariesOverrideSpecificationException(sprintf('drupalSettings may not be overridden in libraries-override. Trying to override %s. Use hook_library_info_alter() instead.', "$extension/$library_name/$sub_key"));
+                throw new InvalidLibrariesOverrideSpecificationException(sprintf('drupalSettings may not be overridden in libraries-override. Trying to override %s. Use hook_library_info_alter() instead.', "$extension/$library_name/$type"));
               }
-              elseif ($sub_key === 'css') {
+              elseif ($type === 'css') {
                 // SMACSS category should be incorporated into the asset name.
                 foreach ($value as $category => $overrides) {
-                  $this->setOverrideValue($libraries[$library_name], [$sub_key, $category], $overrides, $theme_path);
+                  $this->setOverrideValue($overrides, $type, $library_name, $extension, $theme_path);
                 }
               }
               else {
-                $this->setOverrideValue($libraries[$library_name], [$sub_key], $value, $theme_path);
+                $this->setOverrideValue($value, $type, $library_name, $extension, $theme_path);
               }
             }
           }
@@ -427,37 +455,39 @@ protected function isValidUri($string) {
   }
 
   /**
-   * Overrides the specified library asset.
+   * Stores the specified library-overrides for later implementation.
    *
-   * @param array $library
-   *   The containing library definition.
-   * @param array $sub_key
-   *   An array containing the sub-keys specifying the library asset, e.g.
-   *   @code['js']@endcode or @code['css', 'component']@endcode
    * @param array $overrides
    *   Specifies the overrides, this is an array where the key is the asset to
    *   be overridden while the value is overriding asset.
+   * @param string $type
+   *   The type of library asset, e.g. 'js' or 'css'.
+   * @param string $library_name
+   *   The name of the library being overridden.
+   * @param string $extension
+   *   The extension name.
+   * @param string $theme_path
+   *   The path to the theme defining the libraries-override.
    */
-  protected function setOverrideValue(array &$library, array $sub_key, array $overrides, $theme_path) {
+  protected function setOverrideValue(array $overrides, $type, $library_name, $extension, $theme_path) {
     foreach ($overrides as $original => $replacement) {
-      // Get the attributes of the asset to be overridden. If the key does
-      // not exist, then throw an exception.
-      $key_exists = NULL;
-      $parents = array_merge($sub_key, [$original]);
-      // Save the attributes of the library asset to be overridden.
-      $attributes = NestedArray::getValue($library, $parents, $key_exists);
-      if ($key_exists) {
-        // Remove asset to be overridden.
-        NestedArray::unsetValue($library, $parents);
-        // No need to replace if FALSE is specified, since that is a removal.
-        if ($replacement) {
-          // Ensure the replacement path is relative to drupal root.
-          $replacement = $this->resolveThemeAssetPath($theme_path, $replacement);
-          $new_parents = array_merge($sub_key, [$replacement]);
-          // Replace with an override if specified.
-          NestedArray::setValue($library, $new_parents, $attributes);
-        }
+      // $original can either be the last overridden path or the original
+      // library definition path.
+
+      // For BC we check if $original still refers to base-theme overrides.
+      // @todo Remove BC in Drupal 9.0.0 https://www.drupal.org/node/2852314.
+      if (isset($this->originalLibraryPaths[$original])) {
+        // Here $original actually refers to an overridden path (maybe from a
+        // base theme), so get the actual original path by which the library
+        // asset was keyed.
+        @trigger_error('Overriding a library asset using an overridden path as key is deprecated, please use the original path as key.', E_USER_DEPRECATED);
+        $original = $this->originalLibraryPaths[$original];
+      }
+      if ($replacement) {
+        $this->originalLibraryPaths[$this->resolveThemeAssetPath($theme_path, $replacement)] = $original;
       }
+
+      $this->setLatestOverridePath($this->resolveThemeAssetPath($theme_path, $replacement), $original, $type, $library_name, $extension);
     }
   }
 
@@ -466,13 +496,17 @@ protected function setOverrideValue(array &$library, array $sub_key, array $over
    *
    * @param string $theme_path
    *   The theme or base theme.
-   * @param string $overriding_asset
-   *   The overriding library asset.
+   * @param string|false $overriding_asset
+   *   The overriding library asset or false for asset removal.
    *
-   * @return string
-   *   A fully resolved theme asset path relative to the Drupal directory.
+   * @return string|false
+   *   A fully resolved theme asset path relative to the Drupal directory or
+   *   false if the asset is to be removed.
    */
   protected function resolveThemeAssetPath($theme_path, $overriding_asset) {
+    if ($overriding_asset == FALSE) {
+      return FALSE;
+    }
     if ($overriding_asset[0] !== '/' && !$this->isValidUri($overriding_asset)) {
       // The destination is not an absolute path and it's not a URI (e.g.
       // public://generated_js/example.js or http://example.com/js/my_js.js), so
@@ -512,4 +546,47 @@ public static function validateCssLibrary($library) {
     return 0;
   }
 
+  /**
+   * Gets the libraries-override path that applies to the library asset.
+   *
+   * @param string $original_path
+   *   The original library asset source path.
+   * @param string $type
+   *   The type of library asset, e.g. 'js' or 'css'.
+   * @param string $library_name
+   *   The library name or ID string.
+   * @param string $extension
+   *   The extension name.
+   *
+   * @return string|false
+   *   The full path to the effective libraries-override asset or $original_path
+   *   if the asset is not overridden. Returns false if the asset is to be
+   *   removed.
+   */
+  protected function getLatestOverridePath($original_path, $type, $library_name, $extension) {
+    $key = $extension . ':' . $library_name . ':' . $type . ':' . $original_path;
+    return isset($this->overriddenLibraryPaths[$key])
+      ? $this->overriddenLibraryPaths[$key]
+      : $original_path;
+  }
+
+  /**
+   * Sets the libraries-override path that applies to the library asset.
+   *
+   * @param string|false $new_path
+   *   The Drupal-root-relative path to the overriding library asset or false if
+   *   the asset is to be removed.
+   * @param string $original_path
+   *   The original library asset source path.
+   * @param string $type
+   *   The type of library asset, e.g. 'js' or 'css'.
+   * @param string $library_name
+   *   The library name or ID string.
+   * @param string $extension
+   *   The extension name.
+   */
+  protected function setLatestOverridePath($new_path, $original_path, $type, $library_name, $extension) {
+    $this->overriddenLibraryPaths[$extension . ':' . $library_name . ':' . $type . ':' . $original_path] = $new_path;
+  }
+
 }
diff --git a/core/lib/Drupal/Core/Theme/ThemeInitialization.php b/core/lib/Drupal/Core/Theme/ThemeInitialization.php
index 0bf20d7e8e..d5fbb9868d 100644
--- a/core/lib/Drupal/Core/Theme/ThemeInitialization.php
+++ b/core/lib/Drupal/Core/Theme/ThemeInitialization.php
@@ -190,8 +190,9 @@ public function getActiveTheme(Extension $theme, array $base_themes = []) {
     // modules.
     $values['libraries_override'] = [];
 
-    // Get libraries overrides declared by base themes.
-    foreach ($base_themes as $base) {
+    // Get libraries overrides declared by base themes. Reverse list to override
+    // from parent to child.
+    foreach (array_reverse($base_themes) as $base) {
       if (!empty($base->info['libraries-override'])) {
         foreach ($base->info['libraries-override'] as $library => $override) {
           $values['libraries_override'][$base->getPath()][$library] = $override;
diff --git a/core/modules/system/tests/src/Kernel/Theme/ThemeTest.php b/core/modules/system/tests/src/Kernel/Theme/ThemeTest.php
index 49b723b285..9e1756e1ab 100644
--- a/core/modules/system/tests/src/Kernel/Theme/ThemeTest.php
+++ b/core/modules/system/tests/src/Kernel/Theme/ThemeTest.php
@@ -114,7 +114,7 @@ public function testListThemes() {
     // Check if ThemeHandlerInterface::listInfo() returns disabled themes.
     // Check for base theme and subtheme lists.
     $base_theme_list = ['test_basetheme' => 'Theme test base theme'];
-    $sub_theme_list = ['test_subsubtheme' => 'Theme test subsubtheme', 'test_subtheme' => 'Theme test subtheme'];
+    $sub_theme_list = ['test_legacysubtheme' => 'Theme test legacysubtheme', 'test_subsubtheme' => 'Theme test subsubtheme', 'test_subtheme' => 'Theme test subtheme'];
 
     $this->assertIdentical($themes['test_basetheme']->sub_themes, $sub_theme_list, 'Base theme\'s object includes list of subthemes.');
     $this->assertIdentical($themes['test_subtheme']->base_themes, $base_theme_list, 'Subtheme\'s object includes list of base themes.');
diff --git a/core/modules/system/tests/themes/test_basetheme/test_basetheme.info.yml b/core/modules/system/tests/themes/test_basetheme/test_basetheme.info.yml
index 3efb45f3d6..1bcf4b90b4 100644
--- a/core/modules/system/tests/themes/test_basetheme/test_basetheme.info.yml
+++ b/core/modules/system/tests/themes/test_basetheme/test_basetheme.info.yml
@@ -18,6 +18,14 @@ libraries-override:
     css:
       component:
         assets/vendor/farbtastic/farbtastic.css: css/farbtastic.css
+  core/normalize:
+    css:
+        base:
+          assets/vendor/normalize-css/normalize.css: css/normalize.css
+  core/jquery.ui:
+    css:
+      component:
+        assets/vendor/jquery.ui/themes/base/core.css: css/core.css
 
 libraries-extend:
   classy/base:
diff --git a/core/modules/system/tests/themes/test_basetheme/test_basetheme.libraries.yml b/core/modules/system/tests/themes/test_basetheme/test_basetheme.libraries.yml
index b3d34064c4..bdcc97bd49 100644
--- a/core/modules/system/tests/themes/test_basetheme/test_basetheme.libraries.yml
+++ b/core/modules/system/tests/themes/test_basetheme/test_basetheme.libraries.yml
@@ -4,5 +4,6 @@ global-styling:
     base:
       base-add.css: {}
       base-add.sub-remove.css: {}
+      ensure-order.css: {}
       samename.css: {}
       css/base-libraries-extend.css: {}
diff --git a/core/modules/system/tests/themes/test_legacysubtheme/test_legacysubtheme.info.yml b/core/modules/system/tests/themes/test_legacysubtheme/test_legacysubtheme.info.yml
new file mode 100644
index 0000000000..49afc506e4
--- /dev/null
+++ b/core/modules/system/tests/themes/test_legacysubtheme/test_legacysubtheme.info.yml
@@ -0,0 +1,12 @@
+name: 'Theme test legacysubtheme'
+type: theme
+description: 'Test theme which uses test_subtheme as the base theme.'
+version: VERSION
+core: 8.x
+base theme: test_subtheme
+
+libraries-override:
+  core/jquery.farbtastic:
+    css:
+      component:
+        /core/modules/system/tests/themes/test_basetheme/css/farbtastic.css: css/legacysubtheme-farbtastic.css
diff --git a/core/modules/system/tests/themes/test_subsubtheme/test_subsubtheme.info.yml b/core/modules/system/tests/themes/test_subsubtheme/test_subsubtheme.info.yml
index 7bf373a25a..ced35e8d46 100644
--- a/core/modules/system/tests/themes/test_subsubtheme/test_subsubtheme.info.yml
+++ b/core/modules/system/tests/themes/test_subsubtheme/test_subsubtheme.info.yml
@@ -4,3 +4,12 @@ description: 'Test theme which uses test_subtheme as the base theme.'
 version: VERSION
 core: 8.x
 base theme: test_subtheme
+
+libraries-override:
+  core/drupal.dialog:
+    js:
+      misc/dialog/dialog.js: js/subsubtheme-dialog.js
+  core/normalize:
+    css:
+      base:
+        assets/vendor/normalize-css/normalize.css: false
diff --git a/core/modules/system/tests/themes/test_subtheme/test_subtheme.info.yml b/core/modules/system/tests/themes/test_subtheme/test_subtheme.info.yml
index b217374234..1a88337be9 100644
--- a/core/modules/system/tests/themes/test_subtheme/test_subtheme.info.yml
+++ b/core/modules/system/tests/themes/test_subtheme/test_subtheme.info.yml
@@ -9,6 +9,15 @@ libraries:
 stylesheets-remove:
   - '@theme_test/css/sub-remove.css'
   - '@test_basetheme/base-add.sub-remove.css'
+libraries-override:
+  core/jquery.ui:
+    css:
+      component:
+        assets/vendor/jquery.ui/themes/base/core.css: css/core.css
+  test_basetheme/global-styling:
+    css:
+      base:
+        ensure-order.css: css/ensure-order.css
 
 libraries-extend:
   classy/base:
diff --git a/core/modules/system/tests/themes/test_theme/test_theme.info.yml b/core/modules/system/tests/themes/test_theme/test_theme.info.yml
index b9660a45f5..4606bc7b75 100644
--- a/core/modules/system/tests/themes/test_theme/test_theme.info.yml
+++ b/core/modules/system/tests/themes/test_theme/test_theme.info.yml
@@ -45,12 +45,12 @@ libraries-override:
   core/drupal.dropbutton:
     css:
       component:
-        /core/themes/stable/css/core/dropbutton/dropbutton.css: /themes/my_theme/css/dropbutton.css
+        misc/dropbutton/dropbutton.css: /themes/my_theme/css/dropbutton.css
   # Use stream wrappers.
   core/drupal.vertical-tabs:
     css:
       component:
-        /core/themes/stable/css/core/vertical-tabs.css: public://my_css/vertical-tabs.css
+        misc/vertical-tabs.css: public://my_css/vertical-tabs.css
   # Use a protocol-relative URI.
   core/jquery.ui:
     css:
diff --git a/core/tests/Drupal/KernelTests/Core/Asset/LibraryDiscoveryIntegrationTest.php b/core/tests/Drupal/KernelTests/Core/Asset/LibraryDiscoveryIntegrationTest.php
index a77adfcdc1..e7e67c3276 100644
--- a/core/tests/Drupal/KernelTests/Core/Asset/LibraryDiscoveryIntegrationTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Asset/LibraryDiscoveryIntegrationTest.php
@@ -147,6 +147,31 @@ public function testLibrariesOverrideOtherAssetLibraryNames() {
     $this->assertAssetInLibrary('http://example.com/my_theme/css/farbtastic.css', 'core', 'jquery.farbtastic', 'css');
   }
 
+  /**
+   * Tests that libraries-override will not affect order of assets.
+   */
+  public function testLibrariesOverrideOverriddenOrder() {
+
+    $this->assertNoAssetInLibrary('core/modules/system/tests/themes/test_subtheme/css/ensure-order.css', 'test_basetheme', 'global-styling', 'css');
+    // Get assets for base_theme.
+    $original_assets = array_column($this->libraryDiscovery->getLibraryByName('test_basetheme', 'global-styling')['css'], 'data');
+
+    // Activate a subtheme with overrides.
+    $this->activateTheme('test_subtheme');
+    // Assert asset is applied in subtheme.
+    $this->assertNoAssetInLibrary('core/modules/system/tests/themes/test_basetheme/ensure-order.css', 'test_basetheme', 'global-styling', 'css');
+    $this->assertAssetInLibrary('core/modules/system/tests/themes/test_subtheme/css/ensure-order.css', 'test_basetheme', 'global-styling', 'css');
+
+    // Get overridden assets.
+    $overridden_assets = array_column($this->libraryDiscovery->getLibraryByName('test_basetheme', 'global-styling')['css'], 'data');
+
+    // Overridden asset should be at same position in array.
+    $this->assertEquals(
+      array_search('core/modules/system/tests/themes/test_basetheme/ensure-order.css', $original_assets, TRUE),
+      array_search('core/modules/system/tests/themes/test_subtheme/css/ensure-order.css', $overridden_assets, TRUE)
+    );
+  }
+
   /**
    * Tests that base theme libraries-override still apply in sub themes.
    */
@@ -160,6 +185,44 @@ public function testBaseThemeLibrariesOverrideInSubTheme() {
     $this->assertAssetInLibrary('core/modules/system/tests/themes/test_basetheme/css/farbtastic.css', 'core', 'jquery.farbtastic', 'css');
   }
 
+  /**
+   * Tests library-override on already overridden libraries.
+   */
+  public function testLibrariesOverrideOverridden() {
+    // Activate a sub-theme that doesn't override a library override.
+    $this->activateTheme('test_subtheme');
+
+    // Assert that effective libraries override is from the test_subsubtheme.
+    $this->assertAssetInLibrary('core/modules/system/tests/themes/test_basetheme/css/farbtastic.css', 'core', 'jquery.farbtastic', 'css');
+    $this->assertAssetInLibrary('core/modules/system/tests/themes/test_basetheme/css/normalize.css', 'core', 'normalize', 'css');
+
+    // Activate a sub-theme that overrides a library override.
+    $this->activateTheme('test_subsubtheme');
+
+    // Assert that effective libraries override is from the test_subsubtheme.
+    $this->assertNoAssetInLibrary('core/modules/system/tests/themes/test_basetheme/css/normalize.css', 'core', 'normalize', 'css');
+    $this->assertNoAssetInLibrary('core/assets/vendor/normalize-css/normalize.css', 'core', 'normalize', 'css');
+    $this->assertAssetInLibrary('core/modules/system/tests/themes/test_subsubtheme/js/subsubtheme-dialog.js', 'core', 'drupal.dialog', 'js');
+
+    // Assert that the override occurs from parent theme to child theme.
+    $this->assertNoAssetInLibrary('core/modules/system/tests/themes/test_basetheme/css/core.css', 'core', 'jquery.ui', 'css');
+    $this->assertAssetInLibrary('core/modules/system/tests/themes/test_subtheme/css/core.css', 'core', 'jquery.ui', 'css');
+  }
+
+  /**
+   * Tests previous behavior of using the last overridden path.
+   *
+   * @group legacy
+   * @expectedDeprecationMessage Overriding a library asset using an overridden path as key is deprecated, please use the original path as key.
+   */
+  public function testLibrariesOverrideLegacyOverride() {
+    // Activate a sub-theme that overrides a library override.
+    $this->activateTheme('test_legacysubtheme');
+    // Assert that effective libraries override is from the test_legacysubtheme.
+    $this->assertNoAssetInLibrary('core/modules/system/tests/themes/test_basetheme/css/farbtastic.css', 'core', 'jquery.farbtastic', 'css');
+    $this->assertAssetInLibrary('core/modules/system/tests/themes/test_legacysubtheme/css/legacysubtheme-farbtastic.css', 'core', 'jquery.farbtastic', 'css');
+  }
+
   /**
    * Tests libraries-extend.
    */
diff --git a/core/tests/Drupal/Tests/Core/Asset/LibraryDiscoveryParserTest.php b/core/tests/Drupal/Tests/Core/Asset/LibraryDiscoveryParserTest.php
index 70fb040df9..95822a93c2 100644
--- a/core/tests/Drupal/Tests/Core/Asset/LibraryDiscoveryParserTest.php
+++ b/core/tests/Drupal/Tests/Core/Asset/LibraryDiscoveryParserTest.php
@@ -558,6 +558,18 @@ public function providerTestCssAssert() {
     ];
   }
 
+  /**
+   * @covers ::getLatestOverridePath
+   * @covers ::setLatestOverridePath
+   */
+  public function testLatestOverridePath() {
+    $latest = $this->libraryDiscoveryParser->getLatestOverridePath('original-path', 'type', 'extension', 'library_name');
+    $this->assertEquals('original-path', $latest);
+    $this->libraryDiscoveryParser->setLatestOverridePath('latest-path', 'original-path', 'type', 'extension', 'library_name');
+    $latest = $this->libraryDiscoveryParser->getLatestOverridePath('original-path', 'type', 'extension', 'library_name');
+    $this->assertEquals('latest-path', $latest);
+  }
+
 }
 
 /**
@@ -585,6 +597,14 @@ public function setFileValidUri($source, $valid) {
     $this->validUris[$source] = $valid;
   }
 
+  public function getLatestOverridePath($original_path, $type, $extension, $library_name) {
+    return parent::getLatestOverridePath($original_path, $type, $extension, $library_name);
+  }
+
+  public function setLatestOverridePath($new_path, $original_path, $type, $extension, $library_name) {
+    parent::setLatestOverridePath($new_path, $original_path, $type, $extension, $library_name);
+  }
+
 }
 
 if (!defined('CSS_AGGREGATE_DEFAULT')) {
diff --git a/core/themes/seven/seven.info.yml b/core/themes/seven/seven.info.yml
index f00d395914..8cebf42a72 100644
--- a/core/themes/seven/seven.info.yml
+++ b/core/themes/seven/seven.info.yml
@@ -25,9 +25,9 @@ libraries-override:
   system/base:
     css:
       component:
-        /core/themes/stable/css/system/components/system-status-counter.css: css/components/system-status-counter.css
-        /core/themes/stable/css/system/components/system-status-report-counters.css: css/components/system-status-report-counters.css
-        /core/themes/stable/css/system/components/system-status-report-general-info.css: css/components/system-status-report-general-info.css
+        css/components/system-status-counter.css: css/components/system-status-counter.css
+        css/components/system-status-report-counters.css: css/components/system-status-report-counters.css
+        css/components/system-status-report-general-info.css: css/components/system-status-report-general-info.css
   core/drupal.vertical-tabs:
     css:
       component: