Dropdowns often work perfectly until they’re placed inside a scrollable panel, where they can get clipped, and half the menu disappears behind the container’s edge. Godstime Aburu explains why this happens and offers practical solutions to fix it.

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Dropdowns inside scrollable containers break due to three interacting browser systems: overflow clipping, stacking contexts, and containing blocks. The post explains why z-index fixes often fail and presents four practical solutions: DOM portals (rendering at document.body level), fixed positioning with JavaScript coordinates, the new CSS Anchor Positioning API with position-try-fallbacks, and simply restructuring the DOM. Each approach has trade-offs, and accessibility concerns like focus management and ARIA attributes must be handled explicitly regardless of which fix is chosen. The HTML Popover API is highlighted as a modern tool that solves layering but not positioning, and works best combined with anchor positioning.

Dropdowns Inside Scrollable Containers: Why They Break And How To Fix Them Properly — Smashing Magazine