Mostly efficient with a lean Quick Reference, but the opening paragraph on user preference and eye strain explains context Claude largely already knows, and the Check/Fix/Explain/Code Review sections repeat similar phrasing — so it earns 'mostly efficient but could be tightened' rather than fully lean.

Gives a concrete technique ('extracting colors to CSS custom properties and redefining them inside a prefers-color-scheme: dark media query') but no executable selectors or examples in the body — concrete guidance is incomplete and deferred to references/rule.md.

The Check/Fix/Explain/Code Review sections give direction for a simple review task, but there are no explicit validation checkpoints (e.g., verify WCAG contrast after switching, re-check the rendered UI), so checkpoints are only implicit.

The body is a concise overview with clearly signaled one-level-deep navigation ('see references/rule.md' plus the rule-page URL), and references/rule.md is a real bundle file — matching 'clear overview with well-signaled one-level-deep references'.

Names multiple concrete actions — 'reviewing stylesheets, component styles, and responsive behavior' and 'Check the rendered layout across breakpoints and interaction states' — matching the 'lists multiple specific concrete actions' anchor rather than the single-domain level 2.

Explicitly answers both what (review/check stylesheets for dark-mode support) and when via a present 'Use when...' clause, so the missing-trigger cap at 2 does not apply.

Includes relevant terms ('dark mode', 'prefers-color-scheme', 'responsive behavior', 'breakpoints') but omits common natural variations users would say ('dark theme', 'night mode', 'light/dark'), and the embedded rule title 'Support dark mode' reads awkwardly as a trigger.

The dark-mode/prefers-color-scheme niche is fairly distinct, but the broad opening 'reviewing stylesheets, component styles' could overlap with generic CSS review skills, so it is only 'somewhat specific' rather than a clear non-conflicting niche.