[code-reflection] RFR: MNISTDemo UI tweak

[Adam Sotona]

MNISTDemo UI adjusted.

![screenshot](https://github.com/user-attachments/assets/a9eaca28-13d7-45f4-9fb3-97f83bff7f38)

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Commit messages:
 - MNISTDemo UI tweak

Changes: https://git.openjdk.org/babylon/pull/327/files
  Webrev: https://webrevs.openjdk.org/?repo=babylon&pr=327&range=00
  Stats: 13 lines in 1 file changed: 4 ins; 6 del; 3 mod
  Patch: https://git.openjdk.org/babylon/pull/327.diff
  Fetch: git fetch https://git.openjdk.org/babylon.git pull/327/head:pull/327

PR: https://git.openjdk.org/babylon/pull/327