Fix plugin-card button overlap on Add Plugins screen (#64686)

[369work]

Summary

This patch fixes the plugin-card button overlap reported in #64686 by
replacing the absolute-positioning-based layout of .plugin-card-top
with a flexbox + container query based one, following the direction
agreed in comment:29 (joedolson) and comment:30 (wildworks): no
position: absolute, no legacy fixed-offset CSS, and a layout that
doesn't depend on button label length.

Only src/wp-admin/css/list-tables.css is touched. No PHP/markup
changes are required.

Root cause

The overlap wasn't a single bug — it was two independent, viewport-based
breakpoint systems drifting out of sync:

1. The outer grid (#the-list) decides how many .plugin-cards fit
   per row (1 column below 782px, 2 columns from 783px, 3 columns from
   1600px, 4 columns from 2300px).
2. The inner layout of .plugin-card-top (icon / title / description /
   action buttons) previously decided its own layout using viewport
   width via @media, not the actual rendered width of the card.

Because a card's real width depends on both the viewport width and the
current column count, a @media rule keyed to viewport width can't
reliably predict how much space is actually available inside a card.
A card in 3-column mode at a wide viewport can be narrower than a card
in 2-column mode at a medium viewport, yet a viewport-based rule treats
them identically. This mismatch is what produced the reported overlaps
at 320px, 481–756px, and again at 1600px+.

Why container queries instead of viewport media queries

container-type: inline-size is added to .plugin-card, and the
internal layout responds to the card's own rendered width via
@container, not the viewport. This removes the dependency on two
unrelated breakpoint systems entirely — the inner layout now always
has an accurate picture of its own available space, regardless of
column count or viewport size.

Browser support: container size queries are supported by all browsers
in Core's official browser support matrix
(last 2 versions of Chrome/Firefox/Safari/Edge/Opera/iOS), so no
fallback is required.

Why 600px as the breakpoint

The action-buttons column only shares a row with the icon+title when
there's enough width for all three to coexist without cramping:

• Card padding: 32px (16px × 2)
• Icon: 128px (fixed)
• Icon–title gap: 20px
• Title (minimum comfortably readable width): ~150px
• Title–button gap: ~20px
• Action button column (accounting for longer translated labels): ~180–200px

Summing these gives roughly 550px as the point where things start to
fit at all, with no margin for longer translations or larger font
settings. 600px was chosen to give a small buffer above that minimum
so the side-by-side layout only activates when there's genuinely
enough room, consistent with the "don't depend on button text length"
principle from comment:29/30.

Icon/title ordering

The icon remains inside the existing <a class="open-plugin-details-modal">
(no markup change). .plugin-card .name h3 a is made a flex container;
the title text becomes an anonymous flex item and .plugin-icon is
placed before it visually via order: -1, keeping the icon clickable
as part of the details link and preserving the existing DOM order.

Testing

Verified visually across 320, 375, 540, 768, 820, 1024, 1200, 1440,
1574, and 1920px viewport widths on the "Add Plugins" (bundled/beta),
single-column, and multi-column (2/3-col) card grids. In all cases:

• Icon and title stay aligned regardless of title length
• Action buttons consistently sit below (narrow cards) or beside
  (wide cards) the icon+title block, with no cards falling into an
  inconsistent in-between state
• No overlapping elements at any tested width

Trac ticket: https://core.trac.wordpress.org/ticket/64686

Use of AI Tools

AI assistance: Yes
Tool(s): Claude (Anthropic)
Model(s): Claude
Used for: Root-cause analysis of the layout bug, CSS implementation (flexbox + container query refactor), and drafting this PR/Trac description. All changes were tested and verified across multiple viewport widths (320–1920px) by me before submission.

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

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Pull request overview

This PR addresses button overlap in the Plugin Install “Add Plugins” screen by refactoring the .plugin-card-top layout from an absolute-positioning approach to a flexbox layout driven by container queries. This aligns the internal card layout with the card’s rendered width (rather than viewport width), preventing breakpoint mismatches that previously caused overlaps.

Changes:

• Adds container-type: inline-size to .plugin-card to enable size-based container queries.
• Replaces .plugin-card-top’s positioning-based layout with a wrapping flex layout (icon/title, actions, description).
• Updates action button list styling to switch between inline and stacked layouts via @container (min-width: 600px).

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[joedolson]

This is certainly going in a better direction - I think using containers to handle the width is a good idea.

However, this style change introduces a significant visual difference that leaves a large amount of empty white space that I don't think is desirable. I think it's going to require some structural changes in order to be feasible.

As I see it, the region with the icon, title, and action buttons needs to be a grid/flex with an order of icon > heading/description > actions. It won't be trivial to achieve the current or similar layout while also ensuring that the h3 is the first item in the card and the icon is clickable, but that's what needs to happen. It might mean needing to remove the icon from the link and give it a scripted event to trigger the heading's link, but have the image itself have aria-hidden. The focus target would change shape, but the ability to trigger the link would be unchanged for keyboard users.