Feature Request: Support for computed styles

Summary

Please add first-class support for retrieving computed CSS styles through the Chrome DevTools MCP server. Today the MCP surface lets an AI agent inspect DOM/attributes and take screenshots, but it cannot read the browser’s computed styles, which are essential for reliable layout/debugging automation.

Why this matters

• LLMs need ground-truth layout data (final box model, visibility, z-index, display/position, resolved colors/margins/paddings) to diagnose “element not visible,” overlap, off-screen placement, or cascade/specificity issues.
• Visual diffs alone miss subtle regressions (1–2px shifts, collapsed margins, inherited font changes).
• Computed styles enable deterministic before/after comparisons during HMR or CI visual checks.

Requested capabilities (minimum viable)

• Get computed styles for a node: resolved values for all properties (option to filter list).
• Get box model metrics: content/padding/border/margin, client/offset/bounding rect, device-pixel-rounded values.
• Visibility diagnostics: isVisible (accounting for display/visibility/opacity/clip/path, 0×0, off-viewport, overflow hidden).
• Inheritance/precedence hints: which rule “wins” (selector + stylesheet URL/line), optional list of overridden declarations.
• Batch mode: request multiple node IDs in one call for perf.
• Diff helper (optional): server returns changed computed properties between two snapshots.

Sketch of API (illustrative)

• dom.getComputedStyles({ nodeId, properties?: string[] }) -> { computed: Record<string,string>, sourceMap?: RuleOrigin[] }
• dom.getBoxModel({ nodeId }) -> { content, padding, border, margin, clientRect, boundingRect }
• dom.getVisibility({ nodeId }) -> { isVisible, reasons: string[] }
• dom.getComputedStylesBatch({ nodeIds: string[] }) -> {...}

Example use cases

• Verify a fix: “Confirm the button’s clickable area is ≥44×44 CSS px and vertically centered in its parent.”
• Root-cause: “Why is .toast not visible after CSS changes?” (visibility + winning rule).
• Regression diff in CI: “List computed properties that changed for #header vs. previous build.”

Start by locating the existing Chrome DevTools MCP tools for DOM or attribute inspection and screenshots; the issue does not name specific files or tests. Compare their node-ID handling and response shapes with the proposed computed-style, box-model, visibility, batch, and optional diff capabilities. Done means the agreed minimum API is implemented with coverage for its returned layout and visibility data.