[9.1] [Lens] Increase z-index for formula widget (#244850) (#245284)

# Backport

This will backport the following commits from `main` to `9.1`:
- [[Lens] Increase z-index for formula widget
(#244850)](#244850)

<!--- Backport version: 9.6.6 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sorenlouv/backport)

<!--BACKPORT [{"author":{"name":"Maria
Iriarte","email":"106958839+mariairiartef@users.noreply.github.com"},"sourceCommit":{"committedDate":"2025-12-04T17:28:08Z","message":"[Lens]
Increase z-index for formula widget (#244850)\n\n## Summary\n\nFix
https://github.com/elastic/kibana/issues/244283\n\nMakes the Lens
formula auto suggestions visible during inline Lens\nediting in
dashboards.\n\n<img width=\"1724\" height=\"1279\" alt=\"Screenshot
2025-12-02 at 08 54
48\"\nsrc=\"https://github.com/user-attachments/assets/a3b84e47-2188-45cf-930d-e7cbb923db3d\"\n/>\n\n###
Checklist\n\n- [x] The PR description includes the appropriate Release
Notes section,\nand the correct `release_note:*` label is applied per
the\n[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)\n-
[x] Review the
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Increase z-index for formula
widget","number":244850,"url":"https://github.com/elastic/kibana/pull/244850","mergeCommit":{"message":"[Lens]
Increase z-index for formula widget (#244850)\n\n## Summary\n\nFix
https://github.com/elastic/kibana/issues/244283\n\nMakes the Lens
formula auto suggestions visible during inline Lens\nediting in
dashboards.\n\n<img width=\"1724\" height=\"1279\" alt=\"Screenshot
2025-12-02 at 08 54
48\"\nsrc=\"https://github.com/user-attachments/assets/a3b84e47-2188-45cf-930d-e7cbb923db3d\"\n/>\n\n###
Checklist\n\n- [x] The PR description includes the appropriate Release
Notes section,\nand the correct `release_note:*` label is applied per
the\n[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)\n-
[x] Review the
[backport\nguidelines](https://docs.google.com/document/d/1VyN5k91e5OVumlc0Gb9RPa3h1ewuPE705nRtioPiTvY/edit?usp=sharing)\nand
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Increase z-index for formula widget (#244850)\n\n## Summary\n\nFix
https://github.com/elastic/kibana/issues/244283\n\nMakes the Lens
formula auto suggestions visible during inline Lens\nediting in
dashboards.\n\n<img width=\"1724\" height=\"1279\" alt=\"Screenshot
2025-12-02 at 08 54
48\"\nsrc=\"https://github.com/user-attachments/assets/a3b84e47-2188-45cf-930d-e7cbb923db3d\"\n/>\n\n###
Checklist\n\n- [x] The PR description includes the appropriate Release
Notes section,\nand the correct `release_note:*` label is applied per
the\n[guidelines](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)\n-
[x] Review the
[backport\nguidelines](https://docs.google.com/document/d/1VyN5k91e5OVumlc0Gb9RPa3h1ewuPE705nRtioPiTvY/edit?usp=sharing)\nand
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BACKPORT-->

Co-authored-by: Maria Iriarte <106958839+mariairiartef@users.noreply.github.com>

Author: kibanamachine

x-pack/platform/plugins/shared/lens/public/datasources/form_based/operations/definitions/formula/editor/formula_editor.tsx

@@ -12,6 +12,7 @@ import {
   LanguageDocumentationPopoverContent,
 } from '@kbn/language-documentation';
 import { css } from '@emotion/react';
+import { css as cssClassName } from '@emotion/css';
 import {
   EuiButtonIcon,
   EuiButtonEmpty,
@@ -156,7 +157,11 @@ export function FormulaEditor({
     const node1 = (overflowDiv1.current = document.createElement('div'));
     node1.setAttribute('data-test-subj', 'lnsFormulaWidget');
     // Monaco CSS is targeted on the monaco-editor class
-    node1.classList.add('lnsFormulaOverflow', 'monaco-editor');
+    node1.classList.add(
+      'lnsFormulaOverflow',
+      'monaco-editor',
+      cssClassName(sharedEditorStyles.overflowWidget(euiThemeContext))
+    );
     document.body.appendChild(node1);
   }
 
@@ -981,18 +986,17 @@ const sharedEditorStyles = {
         }
       }
 
-      .lnsFormulaOverflow {
-        // Needs to be higher than the modal and all flyouts
-        z-index: ${euiTheme.levels.toast} + 1;
-      }
-
       .lnsFormula__editorContent {
         background-color: ${euiTheme.colors.backgroundBasePlain};
         min-height: 0;
         position: relative;
       }
     `;
   },
+  overflowWidget: ({ euiTheme }: UseEuiTheme) => `
+    // Needs to be higher than the modal and all flyouts
+    z-index: ${Number(euiTheme.levels.toast) + 1};
+  `,
   formulaDocs: ({ euiTheme }: UseEuiTheme) => css`
     display: flex;
     flex-direction: column;