overlay-stack

When To Use

Use this pattern when you need to stack several regions into the same grid cell.

HTML

<section class="overlay_stack" aria-label="Map with controls">
    <figure class="overlay_stack_item">Transit map</figure>
    <form class="overlay_stack_item">Route search controls</form>
</section>

CSS

.overlay_stack {
    display: grid;
}

.overlay_stack_item {
    grid-area: 1 / 1;
}

Core Properties

• display, grid-area define the spatial behavior for this pattern.

Properties That Break The Layout If Removed

• Removing display, grid-area changes the pattern from its documented layout responsibility back toward ordinary flow or an unsafe fixed arrangement.

Constraints And Change Points

• fluid responsiveness is part of the contract; change sizing values only when the new minimum, maximum, or wrap point is documented with the pattern.
• Keep the HTML class hooks and CSS selectors in one-to-one agreement.

Scroll Ownership

No internal scroll container.

Accessibility And Source Order Notes

• Semantic role expectation: Preserve the HTML sample's landmark, list, navigation, form, figure, or article roles; layout classes must not replace semantic elements.
• DOM order expectation: Keep semantic elements, DOM order, reading order, and focus order independent from the visual placement created by the layout classes.
• Focus risk: Any interactive descendants follow DOM order; do not use this pattern to create a visual order that keyboard focus cannot follow.
• Scroll expectation: No internal scroll container.
• Cognitive risk: Low: the pattern should preserve ordinary reading flow when semantic order is already correct.

Browser And Fallback Notes

The CSS uses modern grid, flex, intrinsic sizing, logical properties, or positioning. If a target browser cannot support a property, fall back to ordinary block flow before adding decorative or script-driven layout behavior.

Composition Notes

Use overlay_stack as the stable pattern root and compose additional layout behavior outside that root unless the child class is part of the documented relationship.

Anti-patterns

• Do not add color, border, shadow, typography, or animation rules to reusable pattern CSS.
• Do not use this pattern to repair unclear HTML structure; make the DOM roles legible first.

IA Navigation

Parent: Overlay / Exception patterns in Pattern Categories. Next: Layout Recipes for screen-level composition, or return to the Layout Pattern Catalog when choosing another primitive.