Block Manager: Inline z-index values (WordPress#77759)

* Block manager: Inline z-index values

* Simplify

* Add changelogs

Co-authored-by: mirka <0mirka00@git.wordpress.org>
Co-authored-by: ciampo <mciampini@git.wordpress.org>

Author: mirka

packages/base-styles/CHANGELOG.md

@@ -4,7 +4,9 @@
 
 ### Breaking Changes
 
--   Remove the following entries from the `z-index()` helper ([#77753](https://github.com/WordPress/gutenberg/pull/77753), [#77806](https://github.com/WordPress/gutenberg/pull/77806), [#77808](https://github.com/WordPress/gutenberg/pull/77808)):
+-   Remove the following entries from the `z-index()` helper ([#77753](https://github.com/WordPress/gutenberg/pull/77753), [#77759](https://github.com/WordPress/gutenberg/pull/77759), [#77806](https://github.com/WordPress/gutenberg/pull/77806), [#77808](https://github.com/WordPress/gutenberg/pull/77808)):
+    -   `.block-editor-block-manager__category-title`
+    -   `.block-editor-block-manager__disabled-blocks-count`
     -   `.block-library-query-pattern__selection-search`
     -   `.block-library-template-part__selection-search`
     -   `.edit-site-sidebar-navigation-screen__title-icon`

packages/base-styles/_z-index.scss

@@ -123,11 +123,6 @@ $z-layers: (
 	// Show tooltips above NUX tips, wp-admin menus, submenus, and sidebar:
 	".components-tooltip": 1000002,
 
-	// Make sure block manager sticky category titles appear above the options
-	".block-editor-block-manager__category-title": 1,
-	// And block manager sticky disabled block count is higher still
-	".block-editor-block-manager__disabled-blocks-count": 2,
-
 	// Appear under the customizer heading UI, but over anything else.
 	".customize-widgets__topbar": 8,
 

packages/block-editor/CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+### Enhancements
+
+-   `BlockManager`: Add stacking context isolation to category list ([#77759](https://github.com/WordPress/gutenberg/pull/77759)).
+
 ## 15.18.0 (2026-04-29)
 
 ### Enhancements

packages/block-editor/src/components/block-manager/style.scss

@@ -1,6 +1,5 @@
 @use "@wordpress/base-styles/variables" as *;
 @use "@wordpress/base-styles/colors" as *;
-@use "@wordpress/base-styles/z-index" as *;
 
 .block-editor-block-manager__no-results {
 	font-style: italic;
@@ -9,6 +8,7 @@
 }
 
 .block-editor-block-manager__category {
+	isolation: isolate;
 	margin: 0 0 $grid-unit-30 0;
 }
 
@@ -17,7 +17,8 @@
 	top: - $grid-unit-05; // Offsets the top padding on the modal content container
 	padding: $grid-unit-20 0;
 	background-color: $white;
-	z-index: z-index(".block-editor-block-manager__category-title");
+	// Make sure sticky category titles appear above the options.
+	z-index: 1;
 
 	.components-checkbox-control__label {
 		font-weight: 600;

packages/editor/src/components/block-visibility/style.scss

@@ -1,6 +1,5 @@
 @use "@wordpress/base-styles/colors" as *;
 @use "@wordpress/base-styles/variables" as *;
-@use "@wordpress/base-styles/z-index" as *;
 
 .editor-block-visibility__disabled-blocks-count {
 	border: $border-width solid $gray-300;
@@ -13,7 +12,8 @@
 	position: sticky;
 	// When sticking, tuck the top border beneath the modal header border
 	top: ($grid-unit-05 + 1) * -1;
-	z-index: z-index(".block-editor-block-manager__disabled-blocks-count");
+	// Keep the sticky disabled block count above the category items.
+	z-index: 1;
 
 	// Stick the category titles to the bottom
 	~ .block-editor-block-manager__content .block-editor-block-manager__category-title {