CSS Anchor Positioning Polyfill

Anchoring Elements Using CSS

The CSS anchor positioning specification defines anchor positioning, “where a positioned element can size and position itself relative to one or more ‘anchor elements’ elsewhere on the page.” This CSS Anchor Positioning Polyfill supports and is based on this specification.

The proposed anchor() and anchor-size() functions add flexibility to how absolutely positioned elements can be placed within a layout. Instead of being sized and positioned based solely on the position of their containing block, the proposed new functions allow absolutely positioned elements to be placed relative to one or more author-defined anchor elements.

View the polyfill on GitHub or browse open issues.
Find the polyfill on npm.
Browse or open issues related to the specification here or here.

Note: We strive to keep the polyfill up-to-date with ongoing changes to the spec, and we welcome code contributions and financial support to make that happen.

Positioning with `anchor()` [stylesheet]

Target

Anchor

With polyfill applied: Target and Anchor’s right edges line up. Target’s top edge lines up with the bottom edge of the Anchor.

#my-anchor-positioning {
  anchor-name: --my-anchor-positioning;
}

#my-target-positioning {
  position: absolute;
  top: anchor(--my-anchor-positioning bottom);
  right: anchor(--my-anchor-positioning right, 50px);
}

Positioning with `anchor()` [<style> tag]

Target

Anchor

With polyfill applied: Target is positioned at the top left corner of the Anchor.

/* a <style> tag */

#my-anchor-style-tag {
  anchor-name: --my-anchor-style-tag;
}

#my-target-style-tag {
  position: absolute;
  bottom: anchor(--my-anchor-style-tag start);
  right: anchor(--my-anchor-style-tag left);
}

Positioning with `anchor()` [inline styles]

Target

Anchor

With polyfill applied: Target and Anchor’s right edges line up. Target’s top edge lines up with the bottom edge of the Anchor.

/* inline <style> attributes */

/* anchor */

  style="anchor-name: --my-anchor-in-line"

/* target */

  style="
    position: absolute;
    top: anchor(--my-anchor-in-line bottom);
    right: anchor(--my-anchor-in-line right);
  "

Positioning with `anchor()` [ `position-anchor` property]

Anchor A

Target A

Anchor B

Target B

With polyfill applied: Targets are positioned at the top right corner of their respective Anchors.

<div id="my-position-anchor-a" class="anchor">Anchor A</div>
<div id="my-position-target-a" class="target">Target A</div>
<div id="my-position-anchor-b" class="anchor">Anchor B</div>
<div id="my-position-target-b" class="target">Target B</div>

#my-position-target-a {
  position-anchor: --my-position-anchor-a;
}

#my-position-target-b {
  position-anchor: --my-position-anchor-b;
}

.target {
  position: absolute;
  bottom: anchor(top);
  left: anchor(right);
}

#my-position-anchor-a {
  anchor-name: --my-position-anchor-a;
}

#my-position-anchor-b {
  anchor-name: --my-position-anchor-b;
}

Anchoring a `popover`

With polyfill applied: Target is positioned at the bottom right corner of the Anchor.

#my-anchor-popover {
  position: absolute;
  left: 200px;
  anchor-name: --my-anchor-popover;
}

#my-target-popover {
  position: absolute;
  left: anchor(--my-anchor-popover right);
  top: anchor(--my-anchor-popover bottom);
}

Positioning with `anchor()` [anchor name set as CSS custom property]

Anchor

Target

With polyfill applied: Target is positioned at the top left corner of the Anchor.

#my-anchor-name-prop {
  anchor-name: --my-anchor-name-prop;
}

#my-target-name-prop {
  --anchor-var: --my-anchor-name-prop;

  position: absolute;
  right: anchor(var(--anchor-var) left);
  bottom: anchor(var(--anchor-var) top);
}

Positioning using `inside` and `outside` values

Anchor

Target

With polyfill applied: Target’s bottom edge is aligned with Anchor’s bottom edge, and Target’s left edge is aligned with Anchor’s right edge.

#inside-outside .anchor {
  anchor-name: --inside-outside;
}

#inside-outside .target {
  position: absolute;
  position-anchor: --inside-outside;
  left: anchor(outside);
  bottom: anchor(inside);
}

Fallbacks with `position-try-fallbacks`

position-try-fallbacks Anchor

Target

position-try-fallbacks Anchor 2

Target 2

With polyfill applied, the following positions are attempted in order:

Align the bottom, left edge of the target with the top, right edge of its anchor.
Apply flip-block, flipping across the inline axis, and align the top, left edge of the target with the bottom, right edge of its anchor.
Apply flip-inline, flipping across the block axis, and align the bottom, right edge of the target with the top, left edge of its anchor.
Apply flip-start, flipping across a diagonal line from upper left to lower right, and align the top, right edge of the target with the bottom, left edge of its anchor.
When every position overflows, revert to the last successful fallback position if there is one, otherwise revert to the initial base styles.

Note: Early Chromium implementations used position-try-options instead of position-try-fallbacks. We recommend adding both properties, or using the position-try shorthand.

#my-anchor-try-tactics {
  anchor-name: --my-anchor-try-tactics;
}

#my-anchor-try-tactics-2 {
  anchor-name: --my-anchor-try-tactics-2;
}

#my-target-try-tactics {
  position-anchor: --my-anchor-try-tactics;
}

#my-target-try-tactics-2 {
  position-anchor: --my-anchor-try-tactics-2;
}

#my-target-try-tactics,
#my-target-try-tactics-2 {
  position: absolute;
  bottom: anchor(top);
  left: anchor(right);
  position-try-fallbacks: flip-block, flip-inline, flip-start;
}

Fallbacks with `position-try-fallbacks` and `@position-try`

@position-try Anchor

Target

@position-try Anchor 2

Target 2

With polyfill applied, the following positions are attempted in order:

Align the bottom, left edge of the target with the top, left edge of its anchor.
Align the top, left edge of the target with the bottom, left edge of its anchor.
Align the bottom, right edge of the target with the top, right edge of its anchor.
Align the top, right edge of the target with the bottom, right edge of its anchor, and set the height and width of the target to 100px.
When every position overflows, revert to the last successful fallback position if there is one, otherwise revert to the initial base styles.

#my-anchor-fallback {
  anchor-name: --my-anchor-fallback;
}

#my-anchor-fallback-2 {
  anchor-name: --my-anchor-fallback-2;
}

#my-target-fallback {
  position-anchor: --my-anchor-fallback;
}

#my-target-fallback-2 {
  position-anchor: --my-anchor-fallback-2;
}

#my-target-fallback,
#my-target-fallback-2 {
  position: absolute;

  /* First try to align the bottom, left edge of the target
     with the top, left edge of the anchor. */
  bottom: anchor(top);
  left: anchor(left);
  width: anchor-size(width);
  position-try-fallbacks: --bottom-left, --top-right, --bottom-right;
}

@position-try --bottom-left {
  /* Next try to align the top, left edge of the target
     with the bottom, left edge of the anchor. */
  top: anchor(bottom);
  left: anchor(left);
  /* Values set by the initial styles will still be applied
     unless they are explicitly reverted. */
  bottom: revert;
}

@position-try --top-right {
  /* Next try to align the bottom, right edge of the target
     with the top, right edge of the anchor. */
  bottom: anchor(top);
  right: anchor(right);
  left: revert;
  width: revert;
}

@position-try --bottom-right {
  /* Finally, try to align the top, right edge of the target
     with the bottom, right edge of the anchor. */
  top: anchor(bottom);
  right: anchor(right);
  width: 100px;
  height: 100px;
  bottom: revert;
  left: revert;
}

Positioning with combined try tactics

position-try Anchor

Target

With polyfill applied, the following positions are attempted in order:

Align the bottom, left edge of the target with the top, right edge of the anchor.
Apply flip-block flip-inline, flipping across both the block and inline axis, and align the top, right edge of the target with the bottom, left edge of the anchor.
Apply flip-inline --bottom-left-combined, flipping across the block axis, and align the top, right edge of the target with the bottom, right edge of the anchor.
When every position overflows, revert to the last successful fallback position if there is one, otherwise revert to the initial base styles.

#my-anchor-try-tactics-combined {
  anchor-name: --my-anchor-try-tactics-combined;
}

#my-target-try-tactics-combined {
  position: absolute;
  position-anchor: --my-anchor-try-tactics-combined;
  bottom: anchor(top);
  left: anchor(right);
  position-try: flip-block flip-inline, flip-inline --bottom-left-combined;
}

@position-try --bottom-left-combined {
  top: anchor(bottom);
  left: anchor(left);
  bottom: revert;
}

Positioning with `anchor()` [scrolling elements]

Anchor

Inner-anchored Target

Outer-anchored Target

With polyfill applied: The Inner-anchored Target is positioned at the top right corner of the Anchor. The Outer-anchored Target is positioned at the bottom left corner of the Anchor.

#scroll-anchor {
  anchor-name: --scroll-anchor;
}

#inner-anchored {
  position: absolute;
  bottom: anchor(--scroll-anchor top);
  left: anchor(--scroll-anchor end);
}

#outer-anchored {
  position: absolute;
  top: anchor(--scroll-anchor bottom);
  right: anchor(--scroll-anchor start);
}

Positioning with `anchor()` [used in `calc()` function]

Anchor

Target

With polyfill applied: Target’s left edge is 10px left of the Anchor’s right edge). The top edge of the Target is 10px below the bottom edge of the Anchor.

#my-anchor-math {
  anchor-name: --my-anchor-math;
}

#my-target-math {
  --full-math: anchor(--my-anchor-math 100%);
  --full-minus-math: calc(anchor(--my-anchor-math 100%) - 10px);

  position: absolute;
  top: calc(var(--full-math) + 10px);
  left: var(--full-minus-math);
}

Positioning with `anchor()` [passed through CSS custom property]

Anchor

Target

With polyfill applied: Target’s top edge is positioned at 50% of the height of the Anchor. The right edge of the Target lines up with 100% of the width of the Anchor (i.e. the Anchor’s right edge).

#my-anchor {
  anchor-name: --my-anchor;
}

#my-target {
  --center: anchor(--my-anchor 50%);
  --full: anchor(--my-anchor 100%);

  position: absolute;
  top: var(--center);
  right: var(--full);
}

Positioning with `anchor()` [passed through multiple CSS custom properties]

Anchor

Target

With polyfill applied: Target’s left edge is positioned in Anchor’s horizontal center. Target’s bottom edge is 10% above the bottom edge of Anchor.

#my-anchor-props {
  anchor-name: --my-anchor-props;
}

#my-target-props {
  --half: anchor(--my-anchor-props 50%);
  --quarter: calc(var(--half) / 2);
  --tenth: calc(var(--quarter) / 2.5);

  position: absolute;
  left: var(--half);
  bottom: var(--tenth);
}

Positioning with `anchor()` [with duplicate CSS custom properties]

Anchor

Target

With polyfill applied: Target’s top left corner is positioned in the center (vertically and horizontally) of the Anchor.

#anchor-duplicate-custom-props {
  anchor-name: --anchor-duplicate-custom-props;
}

#target-duplicate-custom-props {
  --center: anchor(--anchor-duplicate-custom-props 50%);

  position: absolute;
  top: var(--center);
  left: var(--center);
}

#other {
  --center: anchor(--anchor-duplicate-custom-props 100%);
}

Positioning with `position-area`

Anchor

Target

With polyfill applied: Target is positioned to the top right of the Anchor. See more examples of position-area.

#position-area .anchor {
  anchor-name: --position-area-anchor;
}

#position-area .target {
  position: absolute;
  position-area: top right;
  position-anchor: --position-area-anchor;
}

Sizing with `anchor-size()`

Anchor

Target

With polyfill applied: Target has the same width as the Anchor.

#my-anchor-size {
  anchor-name: --my-anchor;
  width: 5em;
}

#my-target-size {
  width: anchor-size(--my-anchor width);
}

`anchor-size()` on margin and inset

Anchor

Target

With polyfill applied: Target's margin is the height of the anchor, and its right inset is the width of the anchor.

#my-anchor-anchor-size-extended {
  anchor-name: --my-anchor-size-extended;
  resize: both;
  overflow: hidden;
}

#my-target-anchor-size-extended {
  position: absolute;
  position-anchor: --my-anchor-size-extended;
  right: anchor-size(width);
  margin: anchor-size(height);
}

Dynamically update anchors

Anchor

Target

With polyfill applied: Target and Anchor’s right edges line up. Target’s top edge lines up with the bottom edge of the Anchor.

When Anchor width is changed dynamically, Target position updates accordingly.

#my-anchor-update {
  anchor-name: --my-anchor-update;
}

#my-target-update {
  position: absolute;
  right: anchor(--my-anchor-update right);
  top: anchor(--my-anchor-update bottom);
}

Use a list of anchor names

Anchor

Target A

Target B

With polyfill applied: Target A is positioned at Anchor’s top left corner. Target B is positioned at Anchor’s bottom right corner.

#my-anchor-name-list {
  anchor-name: --my-anchor-name-a, --my-anchor-name-b;
}

#my-target-name-list-a {
  position: absolute;
  right: anchor(--my-anchor-name-a left);
  bottom: anchor(--my-anchor-name-a top);
}

#my-target-name-list-b {
  position: absolute;
  left: anchor(--my-anchor-name-b right);
  top: anchor(--my-anchor-name-b bottom);
}

Absolutely positioned anchor

Anchor one

Target one

Anchor two

Target two

With polyfill applied: Target one is positioned at the bottom right corner of Anchor one. Target two is positioned at the bottom right corner of Anchor two.

#my-anchor-absolute-one,
#my-anchor-absolute-two {
  position: absolute;
  anchor-name: --my-anchor-absolute;
}

#my-target-absolute-one,
#my-target-absolute-two {
  position: absolute;
  top: anchor(--my-anchor-absolute bottom);
  left: anchor(--my-anchor-absolute right);
}

Pseudo-element anchor

Anchor

Target

Target is positioned at the bottom right corner of the Anchor’s ::before pseudo-element.

#my-anchor-pseudo-element::before {
  content: '::before';
  anchor-name: --my-anchor-pseudo-element;
}

#my-target-pseudo-element {
  position: absolute;
  position-anchor: --my-anchor-pseudo-element;
  top: anchor(bottom);
  left: anchor(right);
}

Anchor declared in media query

Screen Anchor

Print Anchor

Target

With polyfill applied: Target and Screen Anchor’s right and top edges line up.

@media print {
  #my-print-anchor-media-query {
    anchor-name: --my-anchor-media-query;
  }
}

#my-anchor-media-query {
  anchor-name: --my-anchor-media-query;
}

#my-target-media-query {
  position: absolute;
  top: anchor(--my-anchor-media-query top);
  right: anchor(--my-anchor-media-query right);
}

Manually apply polyfill to specific styles

Anchor

Target 1 (with <style>)

Target 2 (with <link>)

Target 3 (with inline style)

With polyfill applied: Target 1, 2, and 3 are positioned at Anchor’s top-left, top-right, and bottom-right corners respectively.

<style id="my-style-manual-anchor">
  #my-anchor-manual {
    anchor-name: --my-anchor-manual;
  }
</style>
<style id="my-style-manual-style-el">
  #my-target-manual-style-el {
    position: absolute;
    bottom: anchor(--my-anchor-manual top);
    right: anchor(--my-anchor-manual left);
  }
</style>
<link rel="stylesheet" href="/anchor-manual.css" id="my-style-manual-link-el" />
<!--
CSS inside the anchor-manual.css file:

#my-target-manual-link-el {
  position: absolute;
  bottom: anchor(--my-anchor-manual top);
  left: anchor(--my-anchor-manual right);
}
-->

<div id="my-anchor-manual" class="anchor">...</div>
<div id="my-target-manual-style-el" class="target">...</div>
<div id="my-target-manual-link-el" class="target">...</div>
<div id="my-target-manual-inline-style" class="target"
  style="position: absolute;
    top: anchor(--my-anchor-manual bottom);
    left: anchor(--my-anchor-manual right);"
>...</div>

<script>
  polyfill({
    elements: [
      // The <style> element for anchor
      document.getElementById('my-style-manual-anchor'),
      // The <style> element
      document.getElementById('my-style-manual-style-el'),
      // The <link> element
      document.getElementById('my-style-manual-link-el'),
      // The target element with inline styles
      document.getElementById('my-target-manual-inline-style'),
    ],
  });
</script>

Scope an anchor name

List item One▶
Target One
List item Two▶
Target Two
List item Three▶
Target Three
List item Four▶
Target Four
List item Five▶
Target Five

With polyfill applied: Targets are positioned to the right of their corresponding item’s arrow.

#anchor-scope li {
  anchor-scope: --anchor-scope;
}

#anchor-scope .arrow {
  anchor-name: --anchor-scope;
}

#anchor-scope .target {
  position: absolute;
  position-anchor: --anchor-scope;
  left: anchor(right);
  top: anchor(center);
}

Works with CSS @imports

Anchor

Target One

Target Two

With polyfill applied: Target and Anchor text is orange (from styles defined in an imported stylesheet). Target One is positioned at the bottom right corner of the Anchor. The Anchor has an envelope icon on both sides of the text.

Note: Target Two has position-area defined in an imported stylesheet, which is not parsed by the polyfill, so it is not positioned correctly. It should be positioned at the bottom left corner.

@import url('./import-is-imported-url.css') supports(display: grid) screen and (min-width: 400px);
@import './import-is-imported-string.css';

#imports .anchor::after {
  content: url('./mail.svg');
}

/* ./import-is-imported-url.css */
#imports #target-1 {
  color: var(--brand-orange);
}

#imports #target-2 {
  position-area: block-end inline-start;
  color: var(--brand-orange);
}

#imports .anchor::before {
  content: url('./mail.svg');
}

/* ./import-is-imported-string.css */
#imports .anchor {
  color: var(--brand-orange);
}

Anchoring Elements Using CSS

🔗 Positioning with anchor() [stylesheet]

🔗 Positioning with anchor() [<style> tag]

🔗 Positioning with anchor() [inline styles]

🔗 Positioning with anchor() [ position-anchor property]

🔗 Anchoring a popover

🔗 Positioning with anchor() [anchor name set as CSS custom property]

🔗 Positioning using inside and outside values

🔗 Fallbacks with position-try-fallbacks

🔗 Fallbacks with position-try-fallbacks and @position-try

🔗 Positioning with combined try tactics

🔗 Positioning with anchor() [scrolling elements]

🔗 Positioning with anchor() [used in calc() function]

🔗 Positioning with anchor() [passed through CSS custom property]

🔗 Positioning with anchor() [passed through multiple CSS custom properties]

🔗 Positioning with anchor() [with duplicate CSS custom properties]

🔗 Positioning with position-area

🔗 Sizing with anchor-size()

🔗 anchor-size() on margin and inset

🔗 Dynamically update anchors

🔗 Use a list of anchor names

🔗 Absolutely positioned anchor

🔗 Pseudo-element anchor

🔗 Anchor declared in media query

🔗 Manually apply polyfill to specific styles

🔗 Scope an anchor name

🔗 Works with CSS @imports

🔗 Positioning within the shadow DOM

Sponsor OddBird’s OSS Work

Positioning with `anchor()` [stylesheet]

Positioning with `anchor()` [<style> tag]

Positioning with `anchor()` [inline styles]

Positioning with `anchor()` [ `position-anchor` property]

Anchoring a `popover`

Positioning with `anchor()` [anchor name set as CSS custom property]

Positioning using `inside` and `outside` values

Fallbacks with `position-try-fallbacks`

Fallbacks with `position-try-fallbacks` and `@position-try`

Positioning with combined try tactics

Positioning with `anchor()` [scrolling elements]

Positioning with `anchor()` [used in `calc()` function]

Positioning with `anchor()` [passed through CSS custom property]

Positioning with `anchor()` [passed through multiple CSS custom properties]

Positioning with `anchor()` [with duplicate CSS custom properties]

Positioning with `position-area`

Sizing with `anchor-size()`

`anchor-size()` on margin and inset

Dynamically update anchors

Use a list of anchor names

Absolutely positioned anchor

Pseudo-element anchor

Anchor declared in media query

Manually apply polyfill to specific styles

Scope an anchor name

Works with CSS @imports

Positioning within the shadow DOM