OVERFLOW

• Content-height component: reflow at narrower widths and let normal-flow content establish height. Do not constrain it with height: 100%, a fixed height, or absolute positioning of all content.

• Bounded-height component: propagate the height constraint through growing wrappers (min-height: 0 for flex/grid items). Fit the content or give the intended content region overflow: auto; keep essential controls reachable. Choose scrolling only when it suits the requested interaction.

• Carousel or other intentional overflow: contain the oversized track in its own viewport and provide working navigation/scrolling to every item. Treat a requested count such as “show four items at a time” as the default/initial-width presentation unless the user explicitly requires that column count at every width. Each carousel page should still contain that requested group at narrow widths, but its internal layout must reflow so every required item is usable. Stacking or wrapping the current page’s items preserves the group; squeezing them into tiny columns or clipping later items does not. Choose the installation width, gaps, padding, and usable item minimum together so the requested count actually fits at the initial size.

  A container-driven group page can preserve the requested grouping without changing the carousel’s item-count logic:

  cssCopy

  .trackViewport {
    min-width: 0;
    overflow: hidden;
  }
  
  .page {
    box-sizing: border-box;
    display: grid;
    flex: 0 0 100%;
    min-width: 0;
    grid-template-columns: repeat(auto-fit, minmax(min(100%, 220px), 1fr));
    gap: 16px;
  }
  
  .item {
    min-width: 0;
  }

  At a wide initial width, the page uses the requested presentation count. When the component is narrower than a usable item minimum, the same group wraps to fewer columns or a single column and its content-height component grows. Equivalent container-query or wrapping layouts are valid. A fixed repeat(<count>, minmax(0, 1fr)) or percentage basis derived from the count is not sufficient as the only layout for a horizontally resizable component.

Do not apply blanket overflow: hidden/clip to the root or page as a repair. It can hide text, focus indicators, navigation, and overlays while leaving the layout defect intact. Clip a dedicated media/track/decorative region only when that is its intended behavior. Preserve deliberate shadows and overlays.

Remove Intrinsic Sizing Traps

width: 100% and box-sizing: border-box on the root are necessary, but do not constrain descendants. A bare 1fr track has an automatic minimum; three such tracks can exceed the container even when the grid itself is correctly sized.

• Use min-width: 0 on flex/grid items that must shrink, including nested content wrappers. For a fixed column count, use minmax(0, 1fr); still adapt the layout when columns would become too narrow to use.

• Prefer fewer columns or wrapping to squeezing text and controls. A card with a title, text and a button needs about 240px: below a 480px component, such cards take one column, and a button label stays on one line. An intrinsic collection can use the following pattern; the minimum never exceeds its container’s content width:

  cssCopy

  .grid {
    box-sizing: border-box;
    display: grid;
    min-width: 0;
    grid-template-columns: repeat(auto-fit, minmax(min(100%, 280px), 1fr));
    gap: 16px;
  }

  minmax(280px, 1fr) alone still overflows a slot narrower than 280px. This grid is suitable for a wrapping collection, not a substitute for a carousel’s item/navigation contract.

• For user-authored prose, use overflow-wrap: anywhere so a long word or URL cannot widen the layout. It also lets a flex or grid item shrink to one letter: when the component narrows, stack side content (prices, controls) under the text or reduce insets before ordinary words fragment, and reflow instead of shrinking text below body size. Use truncation only when the product intends it and essential content remains available.

• Constrain images/media to the space available; preserve aspect ratio or use an intentional fitted media frame. Check fixed-size media plus adjacent text, padding, borders, and gaps together.

• Let control rows and pagination adapt without losing buttons, focus rings, or usable target sizes. min-width: 0 does not make fixed children or large padding fit by itself.

Adapt to the component’s width, including a narrow slot on a desktop viewport. Do not derive the layout from window.innerWidth or viewport breakpoints. If container queries are needed, establish the query container on an appropriate ancestor; a query cannot restyle its own container based on that container’s size. Do not add size containment on an auto-height component that prevents content from establishing its height.

Review Before Reporting Completion

First inspect the sizing chain in source. Identify the root, growing wrappers, tracks, cards, text, media, and controls; check each constrained axis. Do not infer safety from a CSS keyword or a successful build. Preserve usable semantic grids and intentional scroll tracks.

When a runnable browser preview is available, exercise the actual component:

1. Vary the component container independently of the page viewport. Cover its initial size, 320px (or a documented editor minimum), both sides of layout breakpoints, and a wider slot. Test narrower widths only when the actual host layout or request requires them. For a vertically resizable component, also test a short bounded height; for content height, verify the root grows without overlapping the next block.
2. Use long prose and an unbroken token, larger text, changed padding/borders, and representative item counts. For carousels, test navigation and the longest item; include RTL when direction changes layout or navigation.
3. Compare root/region scrollWidth with clientWidth (allow about 1px for rounding), and inspect descendant bounds. For bounded height, also compare scrollHeight and clientHeight. An intentional scroll region/track may exceed its client size, but its content must remain reachable and contained. Check the component itself: a page ancestor may clip overflow while the document has no horizontal scrollbar. Conversely, shadows/overlays do not automatically mean the content layout is broken.
4. Visually inspect and use the controls/keyboard. Passing geometry checks by clipping required content is a failure. Verify intentional scroll regions are usable with keyboard and touch, focus stays visible, and navigation can reach every item.

Fix confirmed component-owned defects and repeat affected cases. If the first incorrect constraint comes from the host layout, report that boundary instead of masking it inside the component. For existing components, preserve unrelated public props, editor overrides, and behavior.

Report sizes/states tested and any remaining overflow or inaccessible content. If no browser preview or fixture is available, perform the source review and state that rendered resize behavior is unverified; do not claim the resize review passed. Build, typecheck, a11y scans, and manifest generation do not establish that layout fits.