feat(item-option): add inner and container parts (#30929)

Issue number: N/A

---------

## What is the current behavior?
The inner structural elements of item-option are not exposed as shadow parts, preventing users from being able to customize their styles directly.

## What is the new behavior?
- Exposes `inner` and `container` shadow parts
- Adds e2e test coverage for customizing the shadow parts

## Does this introduce a breaking change?
- [ ] Yes
- [x] No

---------

Co-authored-by: Brandy Smith <6577830+brandyscarney@users.noreply.github.com>

core/api.txt

@@ -987,6 +987,8 @@ ion-item-option,css-prop,--background,ios
 ion-item-option,css-prop,--background,md
 ion-item-option,css-prop,--color,ios
 ion-item-option,css-prop,--color,md
+ion-item-option,part,container
+ion-item-option,part,inner
 ion-item-option,part,native
 
 ion-item-options,none

core/src/components/item-option/item-option.tsx

@@ -17,6 +17,8 @@ import type { Color } from '../../interface';
  * @slot end - Content is placed to the right of the option text in LTR, and to the left in RTL.
  *
  * @part native - The native HTML button or anchor element that wraps all child elements.
+ * @part inner - The inner wrapper element that arranges the option content.
+ * @part container - The container element that wraps the start, icon-only, default, and end slots.
  */
 @Component({
   tag: 'ion-item-option',
@@ -109,9 +111,9 @@ export class ItemOption implements ComponentInterface, AnchorInterface, ButtonIn
         })}
       >
         <TagType {...attrs} class="button-native" part="native" disabled={disabled}>
-          <span class="button-inner">
+          <span class="button-inner" part="inner">
             <slot name="top"></slot>
-            <div class="horizontal-wrapper">
+            <div class="horizontal-wrapper" part="container">
               <slot name="start"></slot>
               <slot name="icon-only"></slot>
               <slot></slot>

core/src/components/item-option/test/custom/item-option.e2e.ts

@@ -0,0 +1,80 @@
+import { expect } from '@playwright/test';
+import { configs, test } from '@utils/test/playwright';
+
+/**
+ * This behavior does not vary across modes/directions
+ */
+configs({ directions: ['ltr'], modes: ['md'] }).forEach(({ title, config }) => {
+  test.describe(title('item-option: custom'), () => {
+    test.describe('CSS shadow parts', () => {
+      test('should be able to customize native part', async ({ page }) => {
+        await page.setContent(
+          `
+          <style>
+            ion-item-option::part(native) {
+              background-color: red;
+            }
+          </style>
+
+          <ion-item-option>Option</ion-item-option>
+        `,
+          config
+        );
+
+        const itemOption = page.locator('ion-item-option');
+        const backgroundColor = await itemOption.evaluate((el) => {
+          const shadowRoot = el.shadowRoot;
+          const native = shadowRoot?.querySelector('.button-native');
+          return native ? window.getComputedStyle(native).backgroundColor : '';
+        });
+        expect(backgroundColor).toBe('rgb(255, 0, 0)');
+      });
+
+      test('should be able to customize inner part', async ({ page }) => {
+        await page.setContent(
+          `
+          <style>
+            ion-item-option::part(inner) {
+              background-color: green;
+            }
+          </style>
+
+          <ion-item-option>Option</ion-item-option>
+        `,
+          config
+        );
+
+        const itemOption = page.locator('ion-item-option');
+        const backgroundColor = await itemOption.evaluate((el) => {
+          const shadowRoot = el.shadowRoot;
+          const inner = shadowRoot?.querySelector('.button-inner');
+          return inner ? window.getComputedStyle(inner).backgroundColor : '';
+        });
+        expect(backgroundColor).toBe('rgb(0, 128, 0)');
+      });
+
+      test('should be able to customize container part', async ({ page }) => {
+        await page.setContent(
+          `
+          <style>
+            ion-item-option::part(container) {
+              background-color: blue;
+            }
+          </style>
+
+          <ion-item-option>Option</ion-item-option>
+        `,
+          config
+        );
+
+        const itemOption = page.locator('ion-item-option');
+        const backgroundColor = await itemOption.evaluate((el) => {
+          const shadowRoot = el.shadowRoot;
+          const container = shadowRoot?.querySelector('.horizontal-wrapper');
+          return container ? window.getComputedStyle(container).backgroundColor : '';
+        });
+        expect(backgroundColor).toBe('rgb(0, 0, 255)');
+      });
+    });
+  });
+});