[Vega] fix Vega icon on dark mode (#268693)

## Summary

The Vega logo doesn't shows up correctly in dark mode, this PR fixes it.

Before:
<img width="251" height="273" alt="Screenshot 2026-05-11 at 16 28 26"
src="https://github.com/user-attachments/assets/715ffe0f-115e-4844-b736-63250d03293e"
/>
<img width="294" height="443" alt="Screenshot 2026-05-11 at 16 28 51"
src="https://github.com/user-attachments/assets/9ed93c27-d2b2-45d3-89c5-d30a852a3b44"
/>

After:
<img width="216" height="251" alt="Screenshot 2026-05-11 at 16 27 43"
src="https://github.com/user-attachments/assets/9eabb5e5-0eb9-4f92-891a-539ea057d649"
/>
<img width="246" height="430" alt="Screenshot 2026-05-11 at 16 29 19"
src="https://github.com/user-attachments/assets/c43762cf-91d9-40aa-8105-1e6894376802"
/>

fix #268694

Author: markov00

src/platform/plugins/private/vis_types/vega/public/add_vega_panel_action.tsx

@@ -9,19 +9,20 @@
 
 import React from 'react';
 
-import { EuiIcon, type IconType } from '@elastic/eui';
+import type { IconType } from '@elastic/eui';
+import { EuiIcon } from '@elastic/eui';
 import { ADD_PANEL_VISUALIZATION_GROUP } from '@kbn/embeddable-plugin/public';
 import type { EmbeddableApiContext } from '@kbn/presentation-publishing';
 import { apiHasAppContext } from '@kbn/presentation-publishing';
 
 import type { VegaPluginStartDependencies } from './plugin';
-import VegaLogoSVG from './vega_logo.svg';
 import { vegaVisType } from './vega_type';
+import { VegaIcon } from './vega_icon';
 
 export function getAddVegaPanelAction(deps: VegaPluginStartDependencies) {
   return {
     id: 'addVegaPanelAction',
-    getIconType: () => VegaIcon,
+    getIconType: () => VegaPanelIcon,
     order: 0,
     isCompatible: async () => true,
     execute: async ({ embeddable }: EmbeddableApiContext) => {
@@ -45,6 +46,6 @@ export function getAddVegaPanelAction(deps: VegaPluginStartDependencies) {
   };
 }
 
-export const VegaIcon: IconType = (props) => (
-  <EuiIcon type={VegaLogoSVG} title={vegaVisType.titleInWizard} size="m" {...props} />
+const VegaPanelIcon: IconType = (props) => (
+  <EuiIcon type={VegaIcon} title={vegaVisType.titleInWizard} size="m" {...props} />
 );

src/platform/plugins/private/vis_types/vega/public/vega_icon.tsx

@@ -0,0 +1,20 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the "Elastic License
+ * 2.0", the "GNU Affero General Public License v3.0 only", and the "Server Side
+ * Public License v 1"; you may not use this file except in compliance with, at
+ * your election, the "Elastic License 2.0", the "GNU Affero General Public
+ * License v3.0 only", or the "Server Side Public License, v 1".
+ */
+import React from 'react';
+import type { IconType } from '@elastic/eui';
+
+import { vegaVisType } from './vega_type';
+
+export const VegaIcon: IconType = (props) => (
+  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 303 251" fill="currentColor" {...props}>
+    <title>{vegaVisType.titleInWizard}</title>
+    <path d="M.707.5h84l41.5 115.5-30 114.5 81.5-230h84.5l39.5 84h-58.5l19-84-88 250h-85L.707.5Z" />
+    <path d="m262.207.5-88 250h-85L.707.5h84l41.5 115.5-30 114.5 81.5-230h84.5Zm0 0-19 84h58.5l-39.5-84Z" />
+  </svg>
+);

src/platform/plugins/private/vis_types/vega/public/vega_logo.svg

@@ -23,7 +23,7 @@ import { getInfoMessage } from './components/vega_info_message';
 import { VegaVisEditorComponent } from './components/vega_vis_editor_lazy';
 
 import type { VisParams } from './vega_fn';
-import { VegaIcon } from './add_vega_panel_action';
+import { VegaIcon } from './vega_icon';
 
 export const vegaVisType: VisTypeDefinition<VisParams> = {
   name: 'vega',
@@ -33,7 +33,7 @@ export const vegaVisType: VisTypeDefinition<VisParams> = {
     defaultMessage: 'Use the Vega syntax to create new types of visualizations.',
     description: 'Vega and Vega-Lite are product names and should not be translated',
   }),
-  icon: VegaIcon,
+  icon: VegaIcon, // VegaIcon svg is wrapped into EUIIcon
   group: VisGroups.PROMOTED,
   titleInWizard: i18n.translate('visTypeVega.type.vegaTitleInWizard', {
     defaultMessage: 'Vega',