Fix horizontal overflow on small screens in theme details section

[im3dabasia]

Trac ticket: https://core.trac.wordpress.org/ticket/62647

Description

A margin of 30px was added to the right of the theme screenshots on larger screens (above 650px) to create a gap between the screenshots and the description. However, this margin was not being removed on smaller screens (below 650px), causing an overflow on the x-axis and resulting in a horizontal scroll.

I removed the margin for smaller screens, as it is unnecessary when the screenshots and description are stacked. This change resolves the issue.

Steps to reproduce:

1. WP-Admin >. Appearance > Themes
2. Hover over any theme
3. Click on the 'Theme Details'
4. Notice that there is a margin-right added in the .theme-screenshots class, which is causing an overflow on the x-axis.

Screencast:

Before the patch:

Screen.Recording.2024-12-05.at.11.05.44.AM.mov

After the patch:

Screen.Recording.2024-12-05.at.11.07.29.AM.mov

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[github-actions]

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