[Image] | (UX) | Stop weird shadow on zoomed view in Classroom (#3260)

## Summary:
When you zoom into an image in Khan Academy classroom, it has a weird shadowy outline
around the modal.

This can be easily fixed by using `margin` instead of `padding`.

Issue: https://khanacademy.atlassian.net/browse/LEMS-3897

## Test plan:
Storybook
- Go to `/perseus/?path=/story/widgets-image-widget-demo--image`
- Make sure nothing looks wrong in the Classic theme
- Go to `/perseus/?path=/story/widgets-image-widget-demo--image&globals=theme:thunderblocks`
- Make sure the weird shadow is gone in the Classroom theme

### Before
<img width="707" height="489" alt="Screenshot 2026-02-17 at 3 53 48 PM" src="https://github.com/user-attachments/assets/c390bbe5-4e07-43c4-8049-1a18131979da" />

### After
<img width="693" height="418" alt="Screenshot 2026-02-17 at 3 53 53 PM" src="https://github.com/user-attachments/assets/9e154927-91da-4e27-896a-941eab0e8985" />

Author: nishasy

Reviewers: catandthemachines, mark-fitzgerald, ivyolamit

Required Reviewers:

Approved By: catandthemachines

Checks: ⏭️  1 check has been skipped, ✅ 10 checks were successful

Pull Request URL: #3260

Author: nishasy

.changeset/little-worms-crash.md

@@ -0,0 +1,5 @@
+---
+"@khanacademy/perseus": patch
+---
+
+[Image] | (UX) | Stop weird shadow on zoomed view in Classroom

packages/perseus/src/components/zoomed-image-view.tsx

@@ -92,13 +92,13 @@ const wbStyles = StyleSheet.create({
     dialog: {
         width: "auto",
         height: "auto",
-        // Add padding so that the image doesn't touch the edges
+        // Add margin so that the image doesn't touch the edges
         // of the screen on desktop.
-        padding: sizing.size_320,
+        margin: sizing.size_320,
 
         // Allow the image to touch the edges of the screen on mobile.
         "@media (max-width: 767px)": {
-            padding: 0,
+            margin: 0,
         },
     },
 });