diff --git a/core/themes/classy/templates/block/block--search-form-block.html.twig b/core/themes/classy/templates/block/block--search-form-block.html.twig
index 399ddd7..19b87df 100644
--- a/core/themes/classy/templates/block/block--search-form-block.html.twig
+++ b/core/themes/classy/templates/block/block--search-form-block.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme override for the search form block.
+ * Theme override for the search form block.
  *
  * Available variables:
  * - plugin_id: The ID of the block implementation.
diff --git a/core/themes/classy/templates/block/block--system-branding-block.html.twig b/core/themes/classy/templates/block/block--system-branding-block.html.twig
index f648773..a698825 100644
--- a/core/themes/classy/templates/block/block--system-branding-block.html.twig
+++ b/core/themes/classy/templates/block/block--system-branding-block.html.twig
@@ -2,7 +2,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a branding block.
+ * Theme override for a branding block.
  *
  * Each branding element variable (logo, name, slogan) is only available if
  * enabled in the block configuration.
diff --git a/core/themes/classy/templates/block/block--system-menu-block.html.twig b/core/themes/classy/templates/block/block--system-menu-block.html.twig
index dff7e39..4ca1df3 100644
--- a/core/themes/classy/templates/block/block--system-menu-block.html.twig
+++ b/core/themes/classy/templates/block/block--system-menu-block.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a menu block.
+ * Theme override for a menu block.
  *
  * Available variables:
  * - plugin_id: The ID of the block implementation.
diff --git a/core/themes/classy/templates/block/block.html.twig b/core/themes/classy/templates/block/block.html.twig
index aa750cb..ea33d86 100644
--- a/core/themes/classy/templates/block/block.html.twig
+++ b/core/themes/classy/templates/block/block.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a block.
+ * Theme override to display a block.
  *
  * Available variables:
  * - plugin_id: The ID of the block implementation.
diff --git a/core/themes/classy/templates/content-edit/file-managed-file.html.twig b/core/themes/classy/templates/content-edit/file-managed-file.html.twig
index 9a33ae1..95f1f43 100644
--- a/core/themes/classy/templates/content-edit/file-managed-file.html.twig
+++ b/core/themes/classy/templates/content-edit/file-managed-file.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a file form widget.
+ * Theme override to display a file form widget.
  *
  * Available variables:
  * - element: Form element for the file upload.
diff --git a/core/themes/classy/templates/content-edit/file-upload-help.html.twig b/core/themes/classy/templates/content-edit/file-upload-help.html.twig
index 8fa6b3e..7cfa477 100644
--- a/core/themes/classy/templates/content-edit/file-upload-help.html.twig
+++ b/core/themes/classy/templates/content-edit/file-upload-help.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display help text for file fields.
+ * Theme override to display help text for file fields.
  *
  * Available variables:
  * - descriptions: Lines of help text for uploading a file.
diff --git a/core/themes/classy/templates/content-edit/file-widget-multiple.html.twig b/core/themes/classy/templates/content-edit/file-widget-multiple.html.twig
index 25534a5..8732676 100644
--- a/core/themes/classy/templates/content-edit/file-widget-multiple.html.twig
+++ b/core/themes/classy/templates/content-edit/file-widget-multiple.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a multi file form widget.
+ * Theme override to display a multi file form widget.
  *
  * Available variables:
  * - table: Table of previously uploaded files.
diff --git a/core/themes/classy/templates/content-edit/file-widget.html.twig b/core/themes/classy/templates/content-edit/file-widget.html.twig
index 892ed3d..df970a1 100644
--- a/core/themes/classy/templates/content-edit/file-widget.html.twig
+++ b/core/themes/classy/templates/content-edit/file-widget.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a file widget.
+ * Theme override to display a file widget.
  *
  * Available variables:
  * - element: Form element for the managed file.
diff --git a/core/themes/classy/templates/content-edit/filter-caption.html.twig b/core/themes/classy/templates/content-edit/filter-caption.html.twig
index eb9d248..26cb037 100644
--- a/core/themes/classy/templates/content-edit/filter-caption.html.twig
+++ b/core/themes/classy/templates/content-edit/filter-caption.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a filter caption.
+ * Theme override for a filter caption.
  *
  * Returns HTML for a captioned image, audio, video or other tag.
  *
diff --git a/core/themes/classy/templates/content-edit/filter-guidelines.html.twig b/core/themes/classy/templates/content-edit/filter-guidelines.html.twig
index 9459c1a..b41267c 100644
--- a/core/themes/classy/templates/content-edit/filter-guidelines.html.twig
+++ b/core/themes/classy/templates/content-edit/filter-guidelines.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for guidelines for a text format.
+ * Theme override for guidelines for a text format.
  *
  * Available variables:
  * - format: Contains information about the current text format, including the
diff --git a/core/themes/classy/templates/content-edit/filter-tips.html.twig b/core/themes/classy/templates/content-edit/filter-tips.html.twig
index b17de01..ed4f6d5 100644
--- a/core/themes/classy/templates/content-edit/filter-tips.html.twig
+++ b/core/themes/classy/templates/content-edit/filter-tips.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a set of filter tips.
+ * Theme override for a set of filter tips.
  *
  * Available variables:
  * - tips: Descriptions and a CSS ID in the form of 'module-name/filter-id'
diff --git a/core/themes/classy/templates/content-edit/image-widget.html.twig b/core/themes/classy/templates/content-edit/image-widget.html.twig
index 8bdc5f1..4c87f2c 100644
--- a/core/themes/classy/templates/content-edit/image-widget.html.twig
+++ b/core/themes/classy/templates/content-edit/image-widget.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for an image field widget.
+ * Theme override for an image field widget.
  *
  * Available variables:
  * - attributes: HTML attributes for the containing element.
diff --git a/core/themes/classy/templates/content-edit/node-add-list.html.twig b/core/themes/classy/templates/content-edit/node-add-list.html.twig
index 258d3e6..49a82b0 100644
--- a/core/themes/classy/templates/content-edit/node-add-list.html.twig
+++ b/core/themes/classy/templates/content-edit/node-add-list.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to list node types available for adding content.
+ * Theme override to list node types available for adding content.
  *
  * This list is displayed on the Add content admin page.
  *
diff --git a/core/themes/classy/templates/content-edit/node-edit-form.html.twig b/core/themes/classy/templates/content-edit/node-edit-form.html.twig
index 6d8ac2a..7ca5c95 100644
--- a/core/themes/classy/templates/content-edit/node-edit-form.html.twig
+++ b/core/themes/classy/templates/content-edit/node-edit-form.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a node edit form.
+ * Theme override for a node edit form.
  *
  * Two column template for the node add/edit form.
  *
diff --git a/core/themes/classy/templates/content-edit/text-format-wrapper.html.twig b/core/themes/classy/templates/content-edit/text-format-wrapper.html.twig
index 4e5ff6d..76b4dfd 100644
--- a/core/themes/classy/templates/content-edit/text-format-wrapper.html.twig
+++ b/core/themes/classy/templates/content-edit/text-format-wrapper.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a text format-enabled form element.
+ * Theme override for a text format-enabled form element.
  *
  * Available variables:
  * - children: Text format element children.
diff --git a/core/themes/classy/templates/content/aggregator-item.html.twig b/core/themes/classy/templates/content/aggregator-item.html.twig
index a3cda41..446bf9b 100644
--- a/core/themes/classy/templates/content/aggregator-item.html.twig
+++ b/core/themes/classy/templates/content/aggregator-item.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to present a feed item in an aggregator page.
+ * Theme override to present a feed item in an aggregator page.
  *
  * Available variables:
  * - url: URL to the originating feed item.
diff --git a/core/themes/classy/templates/content/book-node-export-html.html.twig b/core/themes/classy/templates/content/book-node-export-html.html.twig
index 0efa9a7..dbed490 100644
--- a/core/themes/classy/templates/content/book-node-export-html.html.twig
+++ b/core/themes/classy/templates/content/book-node-export-html.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a single node in a printer-friendly outline.
+ * Theme override for a single node in a printer-friendly outline.
  *
  * Available variables:
  * - node: Fully loaded node.
diff --git a/core/themes/classy/templates/content/comment.html.twig b/core/themes/classy/templates/content/comment.html.twig
index ba62e2b..bb29ee8 100644
--- a/core/themes/classy/templates/content/comment.html.twig
+++ b/core/themes/classy/templates/content/comment.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for comments.
+ * Theme override for comments.
  *
  * Available variables:
  * - author: Comment author. Can be a link or plain text.
diff --git a/core/themes/classy/templates/content/mark.html.twig b/core/themes/classy/templates/content/mark.html.twig
index 2798bb0..4cc72f2 100644
--- a/core/themes/classy/templates/content/mark.html.twig
+++ b/core/themes/classy/templates/content/mark.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a marker for new or updated content.
+ * Theme override for a marker for new or updated content.
  *
  * Available variables:
  * - status: Number representing the marker status to display. Use the constants
diff --git a/core/themes/classy/templates/content/node.html.twig b/core/themes/classy/templates/content/node.html.twig
index 76e521c..976062e 100644
--- a/core/themes/classy/templates/content/node.html.twig
+++ b/core/themes/classy/templates/content/node.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a node.
+ * Theme override to display a node.
  *
  * Available variables:
  * - node: Full node entity.
diff --git a/core/themes/classy/templates/content/search-result.html.twig b/core/themes/classy/templates/content/search-result.html.twig
index 732489b..c952196 100644
--- a/core/themes/classy/templates/content/search-result.html.twig
+++ b/core/themes/classy/templates/content/search-result.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for displaying a single search result.
+ * Theme override for displaying a single search result.
  *
  * This template renders a single search result. The list of results is
  * rendered using '#theme' => 'item_list', with suggestions of:
diff --git a/core/themes/classy/templates/content/taxonomy-term.html.twig b/core/themes/classy/templates/content/taxonomy-term.html.twig
index 2fbffa5..7fb89b3 100644
--- a/core/themes/classy/templates/content/taxonomy-term.html.twig
+++ b/core/themes/classy/templates/content/taxonomy-term.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a taxonomy term.
+ * Theme override to display a taxonomy term.
  *
  * Available variables:
  * - url: URL of the current term.
diff --git a/core/themes/classy/templates/dataset/aggregator-feed.html.twig b/core/themes/classy/templates/dataset/aggregator-feed.html.twig
index 1876c45..6a27265 100644
--- a/core/themes/classy/templates/dataset/aggregator-feed.html.twig
+++ b/core/themes/classy/templates/dataset/aggregator-feed.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to present an aggregator feed.
+ * Theme override to present an aggregator feed.
  *
  * The contents are rendered above feed listings when browsing source feeds.
  * For example, "example.com/aggregator/sources/1".
diff --git a/core/themes/classy/templates/dataset/forum-icon.html.twig b/core/themes/classy/templates/dataset/forum-icon.html.twig
index b32b734..c8e6734 100644
--- a/core/themes/classy/templates/dataset/forum-icon.html.twig
+++ b/core/themes/classy/templates/dataset/forum-icon.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a status icon for a forum post.
+ * Theme override to display a status icon for a forum post.
  *
  * Available variables:
  * - attributes: HTML attributes to be applied to the wrapper element.
diff --git a/core/themes/classy/templates/dataset/forum-list.html.twig b/core/themes/classy/templates/dataset/forum-list.html.twig
index 5b41f6a..07d085a 100644
--- a/core/themes/classy/templates/dataset/forum-list.html.twig
+++ b/core/themes/classy/templates/dataset/forum-list.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a list of forums and containers.
+ * Theme override to display a list of forums and containers.
  *
  * Available variables:
  * - forums: A collection of forums and containers to display. It is keyed to
diff --git a/core/themes/classy/templates/dataset/forums.html.twig b/core/themes/classy/templates/dataset/forums.html.twig
index 1bb7c05..9749845 100644
--- a/core/themes/classy/templates/dataset/forums.html.twig
+++ b/core/themes/classy/templates/dataset/forums.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a forum.
+ * Theme override to display a forum.
  *
  * May contain forum containers as well as forum topics.
  *
diff --git a/core/themes/classy/templates/dataset/item-list.html.twig b/core/themes/classy/templates/dataset/item-list.html.twig
index bd71e7f..0ae6a60 100644
--- a/core/themes/classy/templates/dataset/item-list.html.twig
+++ b/core/themes/classy/templates/dataset/item-list.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for an item list.
+ * Theme override for an item list.
  *
  * Available variables:
  * - items: A list of items. Each item contains:
diff --git a/core/themes/classy/templates/dataset/table.html.twig b/core/themes/classy/templates/dataset/table.html.twig
index 3d0252e..6f0fe79 100644
--- a/core/themes/classy/templates/dataset/table.html.twig
+++ b/core/themes/classy/templates/dataset/table.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a table.
+ * Theme override to display a table.
  *
  * Available variables:
  * - attributes: HTML attributes to apply to the <table> tag.
diff --git a/core/themes/classy/templates/dataset/tablesort-indicator.html.twig b/core/themes/classy/templates/dataset/tablesort-indicator.html.twig
index 059805f..3914ac9 100644
--- a/core/themes/classy/templates/dataset/tablesort-indicator.html.twig
+++ b/core/themes/classy/templates/dataset/tablesort-indicator.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for displaying a tablesort indicator.
+ * Theme override for displaying a tablesort indicator.
  *
  * Available variables:
  * - style: Either 'asc' or 'desc', indicating the sorting direction.
diff --git a/core/themes/classy/templates/field/field--comment.html.twig b/core/themes/classy/templates/field/field--comment.html.twig
index 595bc50..930c232 100644
--- a/core/themes/classy/templates/field/field--comment.html.twig
+++ b/core/themes/classy/templates/field/field--comment.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme override for comment fields.
+ * Theme override for comment fields.
  *
  * Available variables:
  * - attributes: HTML attributes for the containing element.
diff --git a/core/themes/classy/templates/field/field--node--created.html.twig b/core/themes/classy/templates/field/field--node--created.html.twig
index 496d6b2..4b29ee2 100644
--- a/core/themes/classy/templates/field/field--node--created.html.twig
+++ b/core/themes/classy/templates/field/field--node--created.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the node created field.
+ * Theme override for the node created field.
  *
  * This is an override of field.html.twig for the node created field. See that
  * template for documentation about its details and overrides.
diff --git a/core/themes/classy/templates/field/field--node--title.html.twig b/core/themes/classy/templates/field/field--node--title.html.twig
index 5b37bfa..2a4ab84 100644
--- a/core/themes/classy/templates/field/field--node--title.html.twig
+++ b/core/themes/classy/templates/field/field--node--title.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the node title field.
+ * Theme override for the node title field.
  *
  * This is an override of field.html.twig for the node title field. See that
  * template for documentation about its details and overrides.
diff --git a/core/themes/classy/templates/field/field--node--uid.html.twig b/core/themes/classy/templates/field/field--node--uid.html.twig
index 0798d7e..837e166 100644
--- a/core/themes/classy/templates/field/field--node--uid.html.twig
+++ b/core/themes/classy/templates/field/field--node--uid.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the node user field.
+ * Theme override for the node user field.
  *
  * This is an override of field.html.twig for the node user field. See that
  * template for documentation about its details and overrides.
diff --git a/core/themes/classy/templates/field/field.html.twig b/core/themes/classy/templates/field/field.html.twig
index 0745f84..12b928e 100644
--- a/core/themes/classy/templates/field/field.html.twig
+++ b/core/themes/classy/templates/field/field.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a field.
+ * Theme override for a field.
  *
  * To override output, copy the "field.html.twig" from the templates directory
  * to your theme's directory and customize it, just like customizing other
diff --git a/core/themes/classy/templates/field/file-link.html.twig b/core/themes/classy/templates/field/file-link.html.twig
index fbbf08b..bba2755 100644
--- a/core/themes/classy/templates/field/file-link.html.twig
+++ b/core/themes/classy/templates/field/file-link.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a link to a file.
+ * Theme override for a link to a file.
  *
  * Available variables:
  * - attributes: The HTML attributes for the containing element.
diff --git a/core/themes/classy/templates/field/image-formatter.html.twig b/core/themes/classy/templates/field/image-formatter.html.twig
index 0283fcc..a77d3e4 100644
--- a/core/themes/classy/templates/field/image-formatter.html.twig
+++ b/core/themes/classy/templates/field/image-formatter.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a formatted image field.
+ * Theme override to display a formatted image field.
  *
  * Available variables:
  * - image: A collection of image data.
diff --git a/core/themes/classy/templates/field/image-style.html.twig b/core/themes/classy/templates/field/image-style.html.twig
index 6d70ade..8b492f0 100644
--- a/core/themes/classy/templates/field/image-style.html.twig
+++ b/core/themes/classy/templates/field/image-style.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for an image using a specific image style.
+ * Theme override for an image using a specific image style.
  *
  * Available variables:
  * - attributes: HTML attributes for the image, including the following:
diff --git a/core/themes/classy/templates/field/image.html.twig b/core/themes/classy/templates/field/image.html.twig
index 2f29304..c16b139 100644
--- a/core/themes/classy/templates/field/image.html.twig
+++ b/core/themes/classy/templates/field/image.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation of an image.
+ * Theme override of an image.
  *
  * Available variables:
  * - attributes: HTML attributes for the img tag.
diff --git a/core/themes/classy/templates/field/link-formatter-link-separate.html.twig b/core/themes/classy/templates/field/link-formatter-link-separate.html.twig
index 16b91ed..8efe37d 100644
--- a/core/themes/classy/templates/field/link-formatter-link-separate.html.twig
+++ b/core/themes/classy/templates/field/link-formatter-link-separate.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation of a link with separate title and URL elements.
+ * Theme override of a link with separate title and URL elements.
  *
  * Available variables:
  * - link: The link that has already been formatted by l().
diff --git a/core/themes/classy/templates/field/time.html.twig b/core/themes/classy/templates/field/time.html.twig
index 521df56..9c8f4be 100644
--- a/core/themes/classy/templates/field/time.html.twig
+++ b/core/themes/classy/templates/field/time.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a date / time element.
+ * Theme override for a date / time element.
  *
  * Available variables
  * - timestamp: (optional) A UNIX timestamp for the datetime attribute. If the
diff --git a/core/themes/classy/templates/form/checkboxes.html.twig b/core/themes/classy/templates/form/checkboxes.html.twig
index 7c56355..473c682 100644
--- a/core/themes/classy/templates/form/checkboxes.html.twig
+++ b/core/themes/classy/templates/form/checkboxes.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a 'checkboxes' #type form element.
+ * Theme override for a 'checkboxes' #type form element.
  *
  * Available variables
  * - attributes: A list of HTML attributes for the wrapper element.
diff --git a/core/themes/classy/templates/form/confirm-form.html.twig b/core/themes/classy/templates/form/confirm-form.html.twig
index d714917..5e59988 100644
--- a/core/themes/classy/templates/form/confirm-form.html.twig
+++ b/core/themes/classy/templates/form/confirm-form.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for confirm form.
+ * Theme override for confirm form.
  *
  * By default this does not alter the appearance of a form at all,
  * but is provided as a convenience for themers.
diff --git a/core/themes/classy/templates/form/container.html.twig b/core/themes/classy/templates/form/container.html.twig
index 6fb8159..c33caa7 100644
--- a/core/themes/classy/templates/form/container.html.twig
+++ b/core/themes/classy/templates/form/container.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation of a container used to wrap child elements.
+ * Theme override of a container used to wrap child elements.
  *
  * Used for grouped form items. Can also be used as a #theme_wrapper for any
  * renderable element, to surround it with a <div> and HTML attributes.
diff --git a/core/themes/classy/templates/form/datetime-form.html.twig b/core/themes/classy/templates/form/datetime-form.html.twig
index bf31668..bd73beb 100644
--- a/core/themes/classy/templates/form/datetime-form.html.twig
+++ b/core/themes/classy/templates/form/datetime-form.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation of a datetime form element.
+ * Theme override of a datetime form element.
  *
  * Available variables:
  * - attributes: HTML attributes for the datetime form element.
diff --git a/core/themes/classy/templates/form/datetime-wrapper.html.twig b/core/themes/classy/templates/form/datetime-wrapper.html.twig
index 45ba069..2adde35 100644
--- a/core/themes/classy/templates/form/datetime-wrapper.html.twig
+++ b/core/themes/classy/templates/form/datetime-wrapper.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation of a datetime form wrapper.
+ * Theme override of a datetime form wrapper.
  *
  * Available variables:
  * - content: The form element to be output, usually a datelist, or datetime.
diff --git a/core/themes/classy/templates/form/details.html.twig b/core/themes/classy/templates/form/details.html.twig
index 17ea820..c6b1468 100644
--- a/core/themes/classy/templates/form/details.html.twig
+++ b/core/themes/classy/templates/form/details.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a details element.
+ * Theme override for a details element.
  *
  * Available variables
  * - attributes: A list of HTML attributes for the details element.
diff --git a/core/themes/classy/templates/form/dropbutton-wrapper.html.twig b/core/themes/classy/templates/form/dropbutton-wrapper.html.twig
index ca0ff7e..d6afada 100644
--- a/core/themes/classy/templates/form/dropbutton-wrapper.html.twig
+++ b/core/themes/classy/templates/form/dropbutton-wrapper.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a dropbutton wrapper.
+ * Theme override for a dropbutton wrapper.
  *
  * Available variables:
  * - children: Contains the child elements of the dropbutton menu.
diff --git a/core/themes/classy/templates/form/field-multiple-value-form.html.twig b/core/themes/classy/templates/form/field-multiple-value-form.html.twig
index f18a853..9ed9d39 100644
--- a/core/themes/classy/templates/form/field-multiple-value-form.html.twig
+++ b/core/themes/classy/templates/form/field-multiple-value-form.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for an individual form element.
+ * Theme override for an individual form element.
  *
  * Available variables for all fields:
  * - multiple: Whether there are multiple instances of the field.
diff --git a/core/themes/classy/templates/form/fieldset.html.twig b/core/themes/classy/templates/form/fieldset.html.twig
index ab6796c..392fa39 100644
--- a/core/themes/classy/templates/form/fieldset.html.twig
+++ b/core/themes/classy/templates/form/fieldset.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a fieldset element and its children.
+ * Theme override for a fieldset element and its children.
  *
  * Available variables:
  * - attributes: HTML attributes for the fieldset element.
diff --git a/core/themes/classy/templates/form/form-element-label.html.twig b/core/themes/classy/templates/form/form-element-label.html.twig
index 6ececd9..c960b87 100644
--- a/core/themes/classy/templates/form/form-element-label.html.twig
+++ b/core/themes/classy/templates/form/form-element-label.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a form element label.
+ * Theme override for a form element label.
  *
  * Available variables:
  * - title: The label's text.
diff --git a/core/themes/classy/templates/form/form-element.html.twig b/core/themes/classy/templates/form/form-element.html.twig
index a961801..1f2c397 100644
--- a/core/themes/classy/templates/form/form-element.html.twig
+++ b/core/themes/classy/templates/form/form-element.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a form element.
+ * Theme override for a form element.
  *
  * Available variables:
  * - attributes: HTML attributes for the containing element.
diff --git a/core/themes/classy/templates/form/form.html.twig b/core/themes/classy/templates/form/form.html.twig
index 2cd1e95..b94d6c7 100644
--- a/core/themes/classy/templates/form/form.html.twig
+++ b/core/themes/classy/templates/form/form.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a 'form' element.
+ * Theme override for a 'form' element.
  *
  * Available variables
  * - attributes: A list of HTML attributes for the wrapper element.
diff --git a/core/themes/classy/templates/form/input.html.twig b/core/themes/classy/templates/form/input.html.twig
index 1409c25..34e8a8c 100644
--- a/core/themes/classy/templates/form/input.html.twig
+++ b/core/themes/classy/templates/form/input.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for an 'input' #type form element.
+ * Theme override for an 'input' #type form element.
  *
  * Available variables:
  * - attributes: A list of HTML attributes for the input element.
diff --git a/core/themes/classy/templates/form/radios.html.twig b/core/themes/classy/templates/form/radios.html.twig
index bf38830..a35ecd8 100644
--- a/core/themes/classy/templates/form/radios.html.twig
+++ b/core/themes/classy/templates/form/radios.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a 'radios' #type form element.
+ * Theme override for a 'radios' #type form element.
  *
  * Available variables
  * - attributes: A list of HTML attributes for the wrapper element.
diff --git a/core/themes/classy/templates/form/select.html.twig b/core/themes/classy/templates/form/select.html.twig
index 21f32ac..af2e123 100644
--- a/core/themes/classy/templates/form/select.html.twig
+++ b/core/themes/classy/templates/form/select.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a select element.
+ * Theme override for a select element.
  *
  * Available variables:
  * - attributes: HTML attributes for the select tag.
diff --git a/core/themes/classy/templates/form/textarea.html.twig b/core/themes/classy/templates/form/textarea.html.twig
index 8a8426d..6eececc 100644
--- a/core/themes/classy/templates/form/textarea.html.twig
+++ b/core/themes/classy/templates/form/textarea.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a 'textarea' #type form element.
+ * Theme override for a 'textarea' #type form element.
  *
  * Available variables
  * - wrapper_attributes: A list of HTML attributes for the wrapper element.
diff --git a/core/themes/classy/templates/layout/book-export-html.html.twig b/core/themes/classy/templates/layout/book-export-html.html.twig
index cbeb3b3..bc05017 100644
--- a/core/themes/classy/templates/layout/book-export-html.html.twig
+++ b/core/themes/classy/templates/layout/book-export-html.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for printed version of book outline.
+ * Theme override for printed version of book outline.
  *
  * Available variables:
  * - title: Top level node title.
diff --git a/core/themes/classy/templates/layout/html.html.twig b/core/themes/classy/templates/layout/html.html.twig
index 888cf2d..a76b5f9 100644
--- a/core/themes/classy/templates/layout/html.html.twig
+++ b/core/themes/classy/templates/layout/html.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the basic structure of a single Drupal page.
+ * Theme override for the basic structure of a single Drupal page.
  *
  * Variables:
  * - logged_in: A flag indicating if user is logged in.
diff --git a/core/themes/classy/templates/layout/maintenance-page.html.twig b/core/themes/classy/templates/layout/maintenance-page.html.twig
index eaae5ab..877b68b 100644
--- a/core/themes/classy/templates/layout/maintenance-page.html.twig
+++ b/core/themes/classy/templates/layout/maintenance-page.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a single Drupal page while offline.
+ * Theme override to display a single Drupal page while offline.
  *
  * All available variables are mirrored in page.html.twig.
  * Some may be blank but they are provided for consistency.
diff --git a/core/themes/classy/templates/layout/page.html.twig b/core/themes/classy/templates/layout/page.html.twig
index 437a11c..a943aeb 100644
--- a/core/themes/classy/templates/layout/page.html.twig
+++ b/core/themes/classy/templates/layout/page.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a single page.
+ * Theme override to display a single page.
  *
  * The doctype, html, head and body tags are not in this template. Instead they
  * can be found in the html.html.twig template in this directory.
diff --git a/core/themes/classy/templates/layout/region.html.twig b/core/themes/classy/templates/layout/region.html.twig
index b2c5471..b3bbf33 100644
--- a/core/themes/classy/templates/layout/region.html.twig
+++ b/core/themes/classy/templates/layout/region.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a region.
+ * Theme override to display a region.
  *
  * Available variables:
  * - content: The content for this region, typically blocks.
diff --git a/core/themes/classy/templates/misc/feed-icon.html.twig b/core/themes/classy/templates/misc/feed-icon.html.twig
index b3c10d1..4cdebf1 100644
--- a/core/themes/classy/templates/misc/feed-icon.html.twig
+++ b/core/themes/classy/templates/misc/feed-icon.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a feed icon.
+ * Theme override for a feed icon.
  *
  * Available variables:
  * - url: An internal system path or a fully qualified external URL of the feed.
diff --git a/core/themes/classy/templates/misc/progress-bar.html.twig b/core/themes/classy/templates/misc/progress-bar.html.twig
index 885a80f..e06e62c 100644
--- a/core/themes/classy/templates/misc/progress-bar.html.twig
+++ b/core/themes/classy/templates/misc/progress-bar.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a progress bar.
+ * Theme override for a progress bar.
  *
  * Note that the core Batch API uses this only for non-JavaScript batch jobs.
  *
diff --git a/core/themes/classy/templates/misc/rdf-metadata.html.twig b/core/themes/classy/templates/misc/rdf-metadata.html.twig
index 4f65294..cb5c8ad 100644
--- a/core/themes/classy/templates/misc/rdf-metadata.html.twig
+++ b/core/themes/classy/templates/misc/rdf-metadata.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for empty spans with RDF attributes.
+ * Theme override for empty spans with RDF attributes.
  *
  * The XHTML+RDFa doctype allows either <span></span> or <span /> syntax to
  * be used, but for maximum browser compatibility, W3C recommends the
diff --git a/core/themes/classy/templates/misc/status-messages.html.twig b/core/themes/classy/templates/misc/status-messages.html.twig
index fb1ebe3..38ea5e8 100644
--- a/core/themes/classy/templates/misc/status-messages.html.twig
+++ b/core/themes/classy/templates/misc/status-messages.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for status messages.
+ * Theme override for status messages.
  *
  * Displays status, error, and warning messages, grouped by type.
  *
diff --git a/core/themes/classy/templates/navigation/book-all-books-block.html.twig b/core/themes/classy/templates/navigation/book-all-books-block.html.twig
index 6160982..9ba00ba 100644
--- a/core/themes/classy/templates/navigation/book-all-books-block.html.twig
+++ b/core/themes/classy/templates/navigation/book-all-books-block.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for rendering book outlines within a block.
+ * Theme override for rendering book outlines within a block.
  *
  * This template is used only when the block is configured to "show block on all
  * pages", which presents multiple independent books on all pages.
diff --git a/core/themes/classy/templates/navigation/book-navigation.html.twig b/core/themes/classy/templates/navigation/book-navigation.html.twig
index abb0d31..c3a60cb 100644
--- a/core/themes/classy/templates/navigation/book-navigation.html.twig
+++ b/core/themes/classy/templates/navigation/book-navigation.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to navigate books.
+ * Theme override to navigate books.
  *
  * Presented under nodes that are a part of book outlines.
  *
diff --git a/core/themes/classy/templates/navigation/book-tree.html.twig b/core/themes/classy/templates/navigation/book-tree.html.twig
index 9f640d0..23ba6cc 100644
--- a/core/themes/classy/templates/navigation/book-tree.html.twig
+++ b/core/themes/classy/templates/navigation/book-tree.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a book tree.
+ * Theme override for a book tree.
  *
  * Returns HTML for a wrapper for a book sub-tree.
  *
diff --git a/core/themes/classy/templates/navigation/breadcrumb.html.twig b/core/themes/classy/templates/navigation/breadcrumb.html.twig
index f6a1705..8bd225b 100644
--- a/core/themes/classy/templates/navigation/breadcrumb.html.twig
+++ b/core/themes/classy/templates/navigation/breadcrumb.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a breadcrumb trail.
+ * Theme override for a breadcrumb trail.
  *
  * Available variables:
  * - breadcrumb: Breadcrumb trail items.
diff --git a/core/themes/classy/templates/navigation/links.html.twig b/core/themes/classy/templates/navigation/links.html.twig
index 56c7ec2..a8d12ae 100644
--- a/core/themes/classy/templates/navigation/links.html.twig
+++ b/core/themes/classy/templates/navigation/links.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a set of links.
+ * Theme override for a set of links.
  *
  * Available variables:
  * - attributes: Attributes for the UL containing the list of links.
diff --git a/core/themes/classy/templates/navigation/menu-local-action.html.twig b/core/themes/classy/templates/navigation/menu-local-action.html.twig
index 0eb03a9..d3f1b9a 100644
--- a/core/themes/classy/templates/navigation/menu-local-action.html.twig
+++ b/core/themes/classy/templates/navigation/menu-local-action.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a single local action link.
+ * Theme override for a single local action link.
  *
  * Available variables:
  * - attributes: HTML attributes for the wrapper element.
diff --git a/core/themes/classy/templates/navigation/menu-local-task.html.twig b/core/themes/classy/templates/navigation/menu-local-task.html.twig
index 5939203..54f1af3 100644
--- a/core/themes/classy/templates/navigation/menu-local-task.html.twig
+++ b/core/themes/classy/templates/navigation/menu-local-task.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a local task link.
+ * Theme override for a local task link.
  *
  * Available variables:
  * - attributes: HTML attributes for the wrapper element.
diff --git a/core/themes/classy/templates/navigation/menu-local-tasks.html.twig b/core/themes/classy/templates/navigation/menu-local-tasks.html.twig
index dce922b..8563153 100644
--- a/core/themes/classy/templates/navigation/menu-local-tasks.html.twig
+++ b/core/themes/classy/templates/navigation/menu-local-tasks.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display primary and secondary local tasks.
+ * Theme override to display primary and secondary local tasks.
  *
  * Available variables:
  * - primary: HTML list items representing primary tasks.
diff --git a/core/themes/classy/templates/navigation/menu.html.twig b/core/themes/classy/templates/navigation/menu.html.twig
index f01ce84..508933a 100644
--- a/core/themes/classy/templates/navigation/menu.html.twig
+++ b/core/themes/classy/templates/navigation/menu.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a menu.
+ * Theme override to display a menu.
  *
  * Available variables:
  * - menu_name: The machine name of the menu.
diff --git a/core/themes/classy/templates/navigation/pager.html.twig b/core/themes/classy/templates/navigation/pager.html.twig
index a7acd5e..88f55dc 100644
--- a/core/themes/classy/templates/navigation/pager.html.twig
+++ b/core/themes/classy/templates/navigation/pager.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to display a pager.
+ * Theme override to display a pager.
  *
  * Available variables:
  * - items: List of pager items.
diff --git a/core/themes/classy/templates/navigation/toolbar.html.twig b/core/themes/classy/templates/navigation/toolbar.html.twig
index 5d2737d..a9224b4 100644
--- a/core/themes/classy/templates/navigation/toolbar.html.twig
+++ b/core/themes/classy/templates/navigation/toolbar.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for the administrative toolbar.
+ * Theme override for the administrative toolbar.
  *
  * Available variables:
  * - attributes: HTML attributes for the wrapper.
diff --git a/core/themes/classy/templates/navigation/vertical-tabs.html.twig b/core/themes/classy/templates/navigation/vertical-tabs.html.twig
index 5b7298b..b02fa94 100644
--- a/core/themes/classy/templates/navigation/vertical-tabs.html.twig
+++ b/core/themes/classy/templates/navigation/vertical-tabs.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for vertical tabs.
+ * Theme override for vertical tabs.
  *
  * Available variables
  * - attributes: A list of HTML attributes for the wrapper element.
diff --git a/core/themes/classy/templates/user/forum-submitted.html.twig b/core/themes/classy/templates/user/forum-submitted.html.twig
index 8d36a51..11286cc 100644
--- a/core/themes/classy/templates/user/forum-submitted.html.twig
+++ b/core/themes/classy/templates/user/forum-submitted.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for a forum post submission string.
+ * Theme override for a forum post submission string.
  *
  * The submission string indicates when and by whom a topic was submitted.
  *
diff --git a/core/themes/classy/templates/user/user.html.twig b/core/themes/classy/templates/user/user.html.twig
index c44448b..e8c1afe 100644
--- a/core/themes/classy/templates/user/user.html.twig
+++ b/core/themes/classy/templates/user/user.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation to present all user data.
+ * Theme override to present all user data.
  *
  * This template is used when viewing a registered user's page,
  * e.g., example.com/user/123. 123 being the user's ID.
diff --git a/core/themes/classy/templates/user/username.html.twig b/core/themes/classy/templates/user/username.html.twig
index 7859376..1622463 100644
--- a/core/themes/classy/templates/user/username.html.twig
+++ b/core/themes/classy/templates/user/username.html.twig
@@ -1,7 +1,7 @@
 {#
 /**
  * @file
- * Default theme implementation for displaying a username.
+ * Theme override for displaying a username.
  *
  * Available variables:
  * - account: The full account information for the user.