fix(challenge-modal): center mobile modal in viewport

Use left: 50% with translateX(-50%) so the dialog stays centered on
mobile instead of offset from a stale static position.

src/components/challenge-modal/__tests__/challenge-modal.test.tsx

@@ -18,6 +18,7 @@ const testState = vi.hoisted(() => ({
   } as Record<string, any>,
   challenges: [] as Array<{ challenge: any; id: number }>,
   commentsByCid: {} as Record<string, { author?: { shortAddress?: string } }>,
+  isMobile: false,
   publicationPreview: 'preview body',
   publicationType: 'post',
   removeChallengeMock: vi.fn(),
@@ -55,7 +56,7 @@ vi.mock('../../../lib/utils/challenge-utils', () => ({
 }));
 
 vi.mock('../../../hooks/use-is-mobile', () => ({
-  default: () => false,
+  default: () => testState.isMobile,
 }));
 
 vi.mock('../../../hooks/use-theme', () => ({
@@ -162,6 +163,7 @@ describe('ChallengeModal', () => {
         },
       },
     };
+    testState.isMobile = false;
     testState.publicationPreview = 'preview body';
     testState.publicationType = 'post';
     testState.removeChallengeMock.mockReset();
@@ -226,6 +228,27 @@ describe('ChallengeModal', () => {
     expect(testState.removeChallengeMock).toHaveBeenCalledOnce();
   });
 
+  it('centers the mobile modal from the viewport instead of its static position', async () => {
+    testState.isMobile = true;
+    Object.defineProperty(window, 'innerWidth', { configurable: true, value: 375 });
+    Object.defineProperty(window, 'innerHeight', { configurable: true, value: 667 });
+    testState.publicationType = 'reply';
+    testState.challenges = [
+      createStoredChallenge({
+        challenge: 'https://spamblocker.bitsocial.net/api/v1/iframe/session-123',
+        type: 'url/iframe',
+      }),
+    ];
+
+    await renderModal();
+
+    const dialog = container.querySelector<HTMLElement>('[role="dialog"]');
+    expect(container.textContent).toContain('wants to open spamblocker.bitsocial.net.');
+    expect(dialog?.style.left).toBe('50%');
+    expect(dialog?.style.top).toBe('0px');
+    expect(dialog?.style.transform).toBe('translate3d(-50%, 134px, 0)');
+  });
+
   it('redacts generated fortune BBCode from challenge publication details', async () => {
     const publication = {
       ...createPublication(),

src/components/challenge-modal/challenge-modal.tsx

@@ -481,8 +481,8 @@ const Challenge = ({ challenge, closeModal, abandonModal }: ChallengeProps) => {
   if (publication?.parentCid) extraTitleParts.push(parentAddress ? `reply ${parentAddress}` : 'reply');
   if (publicationContent && publicationType !== 'vote') extraTitleParts.push(publicationContent);
 
-  const mobileX = isIframeVisible ? 5 : window.innerWidth / 2 - 150;
   const mobileY = isIframeVisible ? Math.max(10, (window.innerHeight - 600) / 2) : window.innerHeight / 2 - 200;
+  const mobileTransform = isIframeVisible ? `translate3d(5px, ${Math.round(mobileY)}px, 0)` : `translate3d(-50%, ${Math.round(mobileY)}px, 0)`;
   const displayCommunityAddress = getDisplayCommunityAddress(shortCommunityAddress, communityAddress) || t('board');
   const iframeConfirmMessage = stripLegacyIframeConfirmDetails(
     t('iframe_challenge_confirm', {
@@ -524,9 +524,9 @@ const Challenge = ({ challenge, closeModal, abandonModal }: ChallengeProps) => {
       aria-modal='true'
       aria-labelledby='challenge-modal-title'
       style={{
-        transform: isMobile
-          ? `translate3d(${Math.round(mobileX)}px, ${Math.round(mobileY)}px, 0)`
-          : `translate3d(${Math.round(initialPosition.x)}px, ${Math.round(initialPosition.y)}px, 0)`,
+        top: 0,
+        left: isMobile && !isIframeVisible ? '50%' : 0,
+        transform: isMobile ? mobileTransform : `translate3d(${Math.round(initialPosition.x)}px, ${Math.round(initialPosition.y)}px, 0)`,
         touchAction: 'none',
       }}
     >