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CSS Anchor Positioning lets a tooltip, menu, or other positioned element follow a chosen element without JavaScript calculations for its coordinates. Name the trigger with anchor-name, associate the positioned element with position-anchor, then place it with position-area or an inset using anchor(). You still need to provide suitable interaction and accessibility behavior, and to check support for the exact features your design uses.
How CSS Anchor Positioning works
An anchor is the element used as a positioning reference. The anchor-positioned element is the absolutely or fixed-positioned element whose location or size is derived from that reference. For an explicit named relationship, assign an anchor-name to the anchor and the matching name to the positioned element with position-anchor.
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That association is not placement by itself: the positioned element also needs a location rule. position-area describes a region relative to the anchor, while anchor() lets an inset value refer to an anchor side. MDN describes use cases including tooltips, infoboxes, form error messages, settings dialogs, and dropdown menus; these are layout patterns, not interaction behavior supplied automatically by CSS. MDN: CSS anchor positioning
A minimal tooltip pattern
This example associates a help message with a button and places it above the button:
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<button class="help-trigger" aria-describedby="help-tip">Help</button>
<div class="help-tip" id="help-tip" role="tooltip">
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</div>.help-trigger {
anchor-name: --help-trigger;
}
.help-tip {
position: absolute;
position-anchor: --help-trigger;
position-area: top;
margin: 0;
}The CSS demonstrates the named association and placement. The HTML attributes are one possible semantic choice, not a universal recipe: choose the relationship and interaction pattern that fit the content. The positioned element must be absolutely or fixed positioned to use these anchor-positioning features. MDN: Using CSS anchor positioning
Place an element with anchor()
For a more explicit inset-based placement, use an anchor side in the corresponding inset axis:
.help-tip {
position: absolute;
position-anchor: --help-trigger;
top: anchor(bottom);
left: anchor(left);
margin: 0;
}Here, top: anchor(bottom) aligns the tooltip’s top inset with the anchor’s bottom side, and left: anchor(left) aligns their left sides. The side must match the inset axis: a vertical inset such as top cannot use the horizontal side left. The function accepts an optional fallback length or percentage if it is invalid. Add a gap with a calculation, for example top: calc(anchor(bottom) + 0.5rem). MDN: anchor() CSS function
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For browser popovers, inspect their default styles when placement seems wrong. MDN notes that default margin and inset values may conflict with the intended position; reset them as needed, such as with margin: 0; inset: auto. MDN: anchor() CSS function
Plan for viewport edges
A tooltip that fits above its trigger in one position may run offscreen when the page scrolls or the trigger approaches a viewport edge. position-try-fallbacks lets you provide alternative placements for the browser to try in order. For a simple top-or-bottom tooltip, a block-axis flip is a compact option:
.help-tip {
position: absolute;
position-anchor: --help-trigger;
position-area: top;
position-try-fallbacks: flip-block;
margin: 0;
}You can also list inline flips, combinations, other position-area values, or custom alternatives declared with @position-try. These are authored options, not a guarantee that the browser will always find a fitting position: if none of the supplied alternatives prevents overflow, the element returns to its initial placement. If content should disappear when it or its anchor is offscreen, consider position-visibility. MDN: Fallback options and conditional hiding for overflow
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If a tooltip has an arrow, flipping the tooltip can also mean the arrow needs to change direction. MDN describes anchored container queries as a way to style descendants according to the active fallback option; this is an additional refinement, not necessary for a basic placement. MDN: Fallback options and conditional hiding for overflow
Avoid anchor-name collisions
position-anchor sets the default anchor for position-area, position-try, anchor(), and anchor-size() when those features do not identify an anchor directly. Naming an anchor inside anchor() can target it for that function, but does not establish the association by itself; use position-anchor or another applicable association mechanism as well.
If multiple anchors have the same name, the last matching anchor in source order is selected. Repeated components can therefore point at an unintended element unless names are scoped or made unique. Anchor Positioning can also derive dimensions with anchor-size(), and different inset properties can refer to multiple named anchors. Those extensions do not change the fact that the positioned element has one default associated anchor for behaviors such as scrolling with the anchor and conditional hiding. MDN: position-anchor CSS property
Choose the right positioning approach for the UI
CSS Anchor Positioning addresses layout tethering. When deciding how to build a particular menu, tooltip, or dialog, consider the target browser range, how many placement alternatives are needed, whether constrained content should flip, resize, or hide, and what will handle semantics and focus behavior. The CSS feature alone does not answer those interaction questions.
Chrome for Developers notes that combining anchor positioning with the Popover API or a <dialog> can let the browser handle focus-navigation corrections even when the content is elsewhere in DOM order. It also suggests aria-details when a genuine semantic relationship needs to connect an anchor and positioned content. These options do not remove the need to choose suitable semantics, opening and closing behavior, keyboard behavior, and assistive-technology relationships for the specific pattern. Chrome for Developers: The CSS anchor positioning API
Check support and provide a fallback
MDN’s current compatibility labels mark anchor() Baseline 2026, with broad availability across current devices and browser versions since January 2026, and position-anchor newly available since September 2026. These are availability signals, not a guarantee that every related property, value, or older browser version behaves identically; MDN notes that support for parts of anchor() varies. Check the compatibility data for the specific features in your implementation and provide a conventional positioning fallback if your audience includes browsers without the required support. MDN: anchor() CSS function · MDN: position-anchor CSS property
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A feature query can guard the anchor-positioning declarations:
@supports (anchor-name: --myanchor) {
/* Anchor-positioning styles */
}This checks support for the tested declaration; it does not establish support for every advanced fallback or sizing feature inside the block. Chrome for Developers also mentions an OddBird polyfill for older browser versions, while warning that it is incomplete and uses outdated syntax. Treat it as an optional compatibility path only after checking its current maintenance and compatibility, not as full browser-feature parity. Chrome for Developers: The CSS anchor positioning API
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