Tiled Gallery: Oveflow issues in Classic Block

### Steps to reproduce the behavior

1. Add a Classic Block
2. Use the media insert tool to add a tiled gallery
3. Preview or publish the page on a smaller screen
4. See error

#### What I expected to happen

I expected the tiled gallery in a classic block to show all the images in it on all screen sizes


#### What actually happened

At some screen sizes images are cut off on the right, overflowing the gallery and are not visible.


### Context

User reported the issue in HC-29437765

#### Is this specific to the applied theme? Which one?

Repeated the issue on Simple and Atomic with both Baskerville 2 and Twenty Twenty-one.

#### Does this happen on simple or atomic sites or both?

Both

#### Is there any console output or error text?

Yes:

#### Level of impact

All WordPress.com sites and WordPress.org sites that use the Tiled Gallery feature in a Classic block

#### Reproducibility (Consistent, Intermittent) Leave empty for consistent.

#### Screenshot / Video: If applicable, add screenshots to help explain your problem.

Reproduce the issue by adding a Tiled Gallery through the Classic Block, then preview or publish it on smaller screens using Simple and Atomic sites with Baskerville 2 and Twenty Twenty-one. Compare the gallery at affected screen sizes and use the reported console output and screenshots to guide the investigation; done means all images remain visible without right-side overflow.

Written by the indexing model from the issue text.