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<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>CSS Anchor Positioning Polyfill Demo</title>
<link rel="stylesheet" href="https://unpkg.com/open-props" />
<link
rel="stylesheet"
href="https://unpkg.com/prismjs@v1.x/themes/prism.css"
/>
<script
src="https://unpkg.com/@oddbird/popover-polyfill@latest/dist/popover.min.js"
crossorigin="anonymous"
defer
></script>
<link rel="stylesheet" href="/demo.css" />
<!-- Included to test invalid stylesheets -->
<link rel="stylesheet" href="/fake.css" />
<link rel="stylesheet" href="/anchor.css" />
<link rel="stylesheet" href="/anchor-positioning.css" />
<link rel="stylesheet" href="/anchor-popover.css" />
<link rel="stylesheet" href="/position-try.css" />
<link rel="stylesheet" href="/position-try-tactics.css" />
<link rel="stylesheet" href="/position-try-tactics-combined.css" />
<link rel="stylesheet" href="/position-anchor.css" />
<link rel="stylesheet" href="/anchor-scroll.css" />
<link rel="stylesheet" href="/anchor-size.css" />
<link rel="stylesheet" href="/anchor-math.css" />
<link rel="stylesheet" href="/anchor-name-custom-prop.css" />
<link rel="stylesheet" href="/anchor-name-list.css" />
<link rel="stylesheet" href="/anchor-custom-props.css" />
<link rel="stylesheet" href="/anchor-duplicate-custom-props.css" />
<link rel="stylesheet" href="/anchor-implicit.css" />
<link rel="stylesheet" href="/anchor-update.css" />
<link rel="stylesheet" href="/anchor-absolute.css" />
<link rel="stylesheet" href="/anchor-pseudo-element.css" />
<link rel="stylesheet" href="/anchor-media-query.css" />
<style>
#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);
}
#anchor-manual .anchor {
inline-size: fit-content;
margin: 3rem auto;
}
</style>
<script type="module">
import polyfill from '/src/index-fn.ts';
const SUPPORTS_ANCHOR_POSITIONING =
'anchorName' in document.documentElement.style;
const btn = document.getElementById('apply-polyfill');
if (!SUPPORTS_ANCHOR_POSITIONING) {
btn.addEventListener('click', () =>
polyfill().then((rules) => {
btn.innerText = 'Polyfill Applied';
btn.setAttribute('disabled', '');
console.log(rules);
}),
);
} else {
btn.innerText = 'No Polyfill Needed';
btn.setAttribute('disabled', '');
console.log(
'anchor-positioning is supported in this browser; polyfill skipped.',
);
}
const updateBtn = document.getElementById('toggle-anchor-width');
const updateAnchor = document.getElementById('my-anchor-update');
updateBtn.addEventListener('click', () => {
if (updateAnchor.getAttribute('data-small')) {
updateAnchor.setAttribute('data-large', true);
updateAnchor.removeAttribute('data-small');
} else {
updateAnchor.setAttribute('data-small', true);
updateAnchor.removeAttribute('data-large');
}
});
function prepareManualPolyfill() {
// anchor style element
const anchorStyleEl = document.createElement('style');
anchorStyleEl.id = 'my-style-manual-anchor';
anchorStyleEl.textContent = [
'#my-anchor-manual {',
'anchor-name: --my-anchor-manual;',
'}',
].join('');
// style element
const styleEl = document.createElement('style');
styleEl.id = 'my-style-manual-style-el';
styleEl.textContent = [
'#my-target-manual-style-el {',
'position: absolute;',
'bottom: anchor(--my-anchor-manual top);',
'right: anchor(--my-anchor-manual left);',
'}',
].join('');
// link element
const linkEl = document.createElement('link');
linkEl.id = 'my-style-manual-link-el';
linkEl.rel = 'stylesheet';
linkEl.href = '/anchor-manual.css';
document.head.append(anchorStyleEl, styleEl, linkEl);
// inline style
document
.getElementById('my-target-manual-inline-style')
?.setAttribute(
'style',
[
'position: absolute',
'top: anchor(--my-anchor-manual bottom)',
'left: anchor(--my-anchor-manual right)',
].join(';'),
);
}
// These event listeners are for E2E testing only
document
.getElementById('prepare-manual-polyfill')
?.addEventListener('click', () => prepareManualPolyfill(), {
once: true,
});
const manualSet1Button = document.getElementById(
'apply-polyfill-manually-set1',
);
manualSet1Button?.addEventListener('click', (e) => {
polyfill({
elements: [
document.getElementById('my-style-manual-anchor'),
document.getElementById('my-style-manual-style-el'),
],
excludeInlineStyles: true,
}).then(() => {
manualSet1Button.setAttribute('disabled', '');
});
});
const manualSet2Button = document.getElementById(
'apply-polyfill-manually-set2',
);
manualSet2Button?.addEventListener('click', (e) => {
polyfill({
elements: [
document.getElementById('my-style-manual-anchor'),
document.getElementById('my-style-manual-link-el'),
document.getElementById('my-target-manual-inline-style'),
],
excludeInlineStyles: true,
}).then(() => {
manualSet2Button.setAttribute('disabled', '');
});
});
const manualSet3Button = document.getElementById(
'apply-polyfill-manually-set3',
);
manualSet3Button?.addEventListener('click', (e) => {
polyfill({
elements: [
document.getElementById('my-style-manual-anchor'),
document.getElementById('my-style-manual-style-el'),
],
}).then(() => {
manualSet3Button.setAttribute('disabled', '');
});
});
const manualBtn = document.getElementById('apply-polyfill-manually');
if (SUPPORTS_ANCHOR_POSITIONING) {
manualBtn.innerText = 'Load Anchor Positioning CSS';
}
manualBtn.addEventListener('click', () => {
prepareManualPolyfill();
if (!SUPPORTS_ANCHOR_POSITIONING) {
polyfill({
elements: [
document.getElementById('my-style-manual-anchor'),
document.getElementById('my-style-manual-link-el'),
document.getElementById('my-style-manual-style-el'),
document.getElementById('my-target-manual-inline-style'),
],
}).then((rules) => {
manualBtn.innerText = 'Polyfill Applied';
manualBtn.setAttribute('disabled', '');
console.log(rules);
});
} else {
manualBtn.innerText = 'Anchor Positioning CSS applied';
console.log(
'anchor-positioning is supported in this browser; polyfill skipped.',
);
}
manualBtn.setAttribute('disabled', '');
});
</script>
<script src="https://unpkg.com/prismjs@v1.x/components/prism-core.min.js"></script>
<script src="https://unpkg.com/prismjs@v1.x/plugins/autoloader/prism-autoloader.min.js"></script>
</head>
<body>
<header>
<h1>CSS Anchor Positioning Polyfill</h1>
<nav>
<span> See also: </span>
<a
href="https://github.com/web-platform-tests/wpt/tree/master/css/css-anchor-position"
target="_blank"
rel="noopener noreferrer"
>WPT examples</a
>
<!-- <a
href="https://anchor-position-wpt.netlify.app/"
target="_blank"
rel="noopener noreferrer"
>WPT results</a
> -->
<a
href="https://w3c.github.io/csswg-drafts/css-anchor-position/"
target="_blank"
rel="noopener noreferrer"
>Draft Spec</a
>
</nav>
<button id="apply-polyfill" data-button="apply-polyfill" type="button">
Apply Polyfill
</button>
</header>
<section>
<h2>Anchoring Elements Using CSS</h2>
<p>
The CSS anchor positioning
<a
href="https://w3c.github.io/csswg-drafts/css-anchor-position/"
target="_blank"
rel="noopener noreferrer"
>specification</a
>
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.
</p>
<p>
The proposed <code>anchor()</code> and
<code>anchor-size()</code> 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.
</p>
<ul>
<li>
View the polyfill on
<a
href="https://github.com/oddbird/css-anchor-positioning"
target="_blank"
rel="noopener noreferrer"
>GitHub</a
>
or browse
<a
href="https://github.com/oddbird/css-anchor-positioning/issues"
target="_blank"
rel="noopener noreferrer"
>open issues</a
>.
</li>
<li>
Find the polyfill on
<a
href="https://www.npmjs.com/package/@oddbird/css-anchor-positioning"
target="_blank"
rel="noopener noreferrer"
>npm</a
>.
</li>
<li>
Browse or open issues related to the specification
<a
href="https://github.com/w3c/csswg-drafts/labels/css-anchor-1"
target="_blank"
rel="noopener noreferrer"
>here</a
>
or
<a
href="https://github.com/tabatkins/specs/issues?q=is%3Aissue+is%3Aopen+%5Bcss-anchor-position%5D"
target="_blank"
rel="noopener noreferrer"
>here</a
>.
</li>
</ul>
<p>
<strong>Note: </strong>This polyfill was implemented against an early
version of the spec, and updates were paused to allow the syntax to
solidify. Now that browsers are working on implementation, we are in the
process of bringing it up to date, and welcome
<a
href="https://github.com/oddbird/css-anchor-positioning"
target="_blank"
rel="noopener noreferrer"
>code contributions</a
>
and <a href="#sponsor">financial support</a> to make that happen.
</p>
</section>
<section id="anchor-positioning" class="demo-item">
<h2>
<a href="#anchor-positioning" aria-hidden="true">🔗</a>
Positioning with <code>anchor()</code> [stylesheet]
</h2>
<div style="position: relative" class="demo-elements">
<div id="my-target-positioning" class="target">Target</div>
<div id="my-anchor-positioning" class="anchor">Anchor</div>
</div>
<p class="note">
With polyfill applied: Target and Anchor's right edges line up. Target's
top edge lines up with the bottom edge of the Anchor.
</p>
<pre><code class="language-css"
>#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);
}</code></pre>
</section>
<section id="anchor-style-tag" class="demo-item">
<h2>
<a href="#anchor-style-tag" aria-hidden="true">🔗</a>
Positioning with <code>anchor()</code> [<style> tag]
</h2>
<div style="position: relative" class="demo-elements">
<div id="my-target-style-tag" class="target">Target</div>
<div id="my-anchor-style-tag" class="anchor">Anchor</div>
</div>
<p class="note">
With polyfill applied: Target is positioned at the top left corner of
the Anchor.
</p>
<pre><code class="language-css"
>/* 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);
}</code></pre>
</section>
<section id="anchor-inline" class="demo-item">
<h2>
<a href="#anchor-inline" aria-hidden="true">🔗</a>
Positioning with <code>anchor()</code> [inline styles]
</h2>
<div style="position: relative" class="demo-elements">
<div
id="my-target-inline"
class="target"
style="
position: absolute;
top: anchor(--my-anchor-in-line bottom);
right: anchor(--my-anchor-in-line right);
"
>
Target
</div>
<div
id="my-anchor-inline"
class="anchor"
style="anchor-name: --my-anchor-in-line"
>
Anchor
</div>
</div>
<p class="note">
With polyfill applied: Target and Anchor's right edges line up. Target's
top edge lines up with the bottom edge of the Anchor.
</p>
<pre><code class="language-css"
>/* 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);
"</code></pre>
</section>
<section id="implicit-name" class="demo-item">
<h2>
<a href="#implicit-name" aria-hidden="true">🔗</a>
Positioning with <code>anchor()</code> [implicit
<code>anchor</code> attribute]
</h2>
<div style="position: relative" class="demo-elements">
<div id="my-implicit-anchor" class="anchor">Anchor</div>
<div id="my-implicit-target" class="target" anchor="my-implicit-anchor">
Target
</div>
</div>
<p class="note">
With polyfill applied: Target is positioned at the top left corner of
the Anchor.
</p>
<pre><code class="language-html"
><div id="my-implicit-anchor">Anchor</div>
<div id="my-implicit-target" anchor="my-implicit-anchor">Target</div></code>
<code class="language-css"
>#my-implicit-target {
position: absolute;
right: anchor(implicit left);
bottom: anchor(top);
}</code></pre>
</section>
<section id="position-anchor" class="demo-item">
<h2>
<a href="#position-anchor" aria-hidden="true">🔗</a>
Positioning with <code>anchor()</code> [
<code>position-anchor</code> property]
</h2>
<div style="position: relative" class="demo-elements">
<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>
</div>
<p class="note">
With polyfill applied: Targets are positioned at the top right corner of
their respective Anchors.
</p>
<pre><code class="language-html"
><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></code>
<code class="language-css"
>#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;
}</code></pre>
</section>
<section id="anchor-positioning-popover" class="demo-item">
<h2>
<a href="#anchor-positioning-popover" aria-hidden="true">🔗</a>
Anchoring a <code>popover</code>
</h2>
<div style="position: relative" class="demo-elements">
<button
id="my-anchor-popover"
class="anchor"
popovertarget="my-target-popover"
>
Anchor (click to open)
</button>
<div id="my-target-popover" class="target" popover>
Popover (Target)
</div>
</div>
<p class="note">
With polyfill applied: Target is positioned at the bottom right corner
of the Anchor.
</p>
<pre><code class="language-css"
>#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);
}</code></pre>
</section>
<section id="custom-prop-name" class="demo-item">
<h2>
<a href="#custom-prop-name" aria-hidden="true">🔗</a>
Positioning with <code>anchor()</code> [anchor name set as CSS custom
property]
</h2>
<div style="position: relative" class="demo-elements">
<div id="my-anchor-name-prop" class="anchor">Anchor</div>
<div id="my-target-name-prop" class="target">Target</div>
</div>
<p class="note">
With polyfill applied: Target is positioned at the top left corner of
the Anchor.
</p>
<pre><code class="language-css"
>#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);
}</code></pre>
</section>
<section id="position-try-tactics" class="demo-item">
<h2>
<a href="#position-try-tactics" aria-hidden="true">🔗</a>
Fallbacks with <code>position-try-fallbacks</code>
</h2>
<div style="position: relative" class="demo-elements">
<div class="scroll-container">
<div class="placefiller-above-anchor"></div>
<div class="placefiller-before-anchor"></div>
<span id="my-anchor-try-tactics" class="anchor"
>position-try-fallbacks Anchor</span
>
<div id="my-target-try-tactics" class="target">Target</div>
<span id="my-anchor-try-tactics-2" class="anchor"
>position-try-fallbacks Anchor 2</span
>
<div id="my-target-try-tactics-2" class="target">Target 2</div>
<div class="placefiller-after-anchor"></div>
</div>
</div>
<div class="note">
<p>
With polyfill applied, the following positions are attempted in order:
</p>
<ol>
<li>
Align the bottom, left edge of the target with the top, right edge
of its anchor.
</li>
<li>
Apply <code>flip-block</code>, flipping across the inline axis, and
align the top, left edge of the target with the bottom, right edge
of its anchor.
</li>
<li>
Apply <code>flip-inline</code>, flipping across the block axis, and
align the bottom, right edge of the target with the top, left edge
of its anchor.
</li>
<li>
Apply <code>flip-start</code>, 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.
</li>
<li>
When every position overflows, revert to the last successful
fallback position if there is one, otherwise revert to the initial
base styles.
</li>
</ol>
<p>
<strong>Note:</strong> Early Chromium implementations used
<code>position-try-options</code> instead of
<code>position-try-fallbacks</code>. We recommend adding both
properties, or using the <code>position-try</code> shorthand.
</p>
</div>
<pre><code class="language-css"
>#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;
}</code></pre>
</section>
<section id="position-try" class="demo-item">
<h2>
<a href="#position-try" aria-hidden="true">🔗</a>
Fallbacks with <code>position-try-fallbacks</code> and
<code>@position-try</code>
</h2>
<div style="position: relative" class="demo-elements">
<div class="scroll-container">
<div class="placefiller-above-anchor"></div>
<div class="placefiller-before-anchor"></div>
<span id="my-anchor-fallback" class="anchor"
>@position-try Anchor</span
>
<div id="my-target-fallback" class="target">Target</div>
<span id="my-anchor-fallback-2" class="anchor"
>@position-try Anchor 2</span
>
<div id="my-target-fallback-2" class="target">Target 2</div>
<div class="placefiller-after-anchor"></div>
</div>
</div>
<div class="note">
<p>
With polyfill applied, the following positions are attempted in order:
</p>
<ol>
<li>
Align the bottom, left edge of the target with the top, left edge of
its anchor.
</li>
<li>
Align the top, left edge of the target with the bottom, left edge of
its anchor.
</li>
<li>
Align the bottom, right edge of the target with the top, right edge
of its anchor.
</li>
<li>
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.
</li>
<li>
When every position overflows, revert to the last successful
fallback position if there is one, otherwise revert to the initial
base styles.
</li>
</ol>
</div>
<pre><code class="language-css"
>#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;
}</code></pre>
</section>
<section id="position-try-tactics-combined" class="demo-item">
<h2>
<a href="#position-try-tactics-combined" aria-hidden="true">🔗</a>
Positioning with combined try tactics
</h2>
<div style="position: relative" class="demo-elements">
<div class="scroll-container">
<div class="placefiller-above-anchor"></div>
<div class="placefiller-before-anchor"></div>
<span id="my-anchor-try-tactics-combined" class="anchor"
>position-try Anchor</span
>
<div id="my-target-try-tactics-combined" class="target">Target</div>
<div class="placefiller-after-anchor"></div>
</div>
</div>
<div class="note">
<p>
With polyfill applied, the following positions are attempted in order:
</p>
<ol>
<li>
Align the bottom, left edge of the target with the top, right edge
of the anchor.
</li>
<li>
Apply <code>flip-block flip-inline</code>, 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.
</li>
<li>
Apply <code>flip-inline --bottom-left-combined</code>, flipping
across the block axis, and align the top, right edge of the target
with the bottom, right edge of the anchor.
</li>
<li>
When every position overflows, revert to the last successful
fallback position if there is one, otherwise revert to the initial
base styles.
</li>
</ol>
</div>
<pre><code class="language-css"
>#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;
}</code></pre>
</section>
<section id="anchor-scroll" class="demo-item">
<h2>
<a href="#anchor-scroll" aria-hidden="true">🔗</a>
Positioning with <code>anchor()</code> [scrolling elements]
</h2>
<div style="position: relative" class="demo-elements">
<div class="scroll-container">
<div class="placefiller-above-anchor"></div>
<div class="placefiller-before-anchor"></div>
<span id="scroll-anchor" class="anchor">Anchor</span>
<div id="inner-anchored" class="target">Inner-anchored Target</div>
<div class="placefiller-after-anchor"></div>
</div>
<div id="outer-anchored" class="target outer-anchored">
Outer-anchored Target
</div>
</div>
<p class="note">
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.
</p>
<pre><code class="language-css"
>#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);
}</code></pre>
</section>
<section id="math-function" class="demo-item">
<h2>
<a href="#math-function" aria-hidden="true">🔗</a>
Positioning with <code>anchor()</code> [used in
<code>calc()</code> function]
</h2>
<div style="position: relative" class="demo-elements">
<div id="my-anchor-math" class="anchor">Anchor</div>
<div id="my-target-math" class="target">Target</div>
</div>
<p class="note">
With polyfill applied: Target's left edge is 50px left of the Anchor's
right edge). The top edge of the Target is 50px above the bottom edge of
the Anchor.
</p>
<pre><code class="language-css"
>#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%) - 50px);
position: absolute;
top: calc(var(--full-math) - 50px);
left: var(--full-minus-math);
}</code></pre>
</section>
<section id="custom-prop" class="demo-item">
<h2>
<a href="#custom-prop" aria-hidden="true">🔗</a>
Positioning with <code>anchor()</code> [passed through CSS custom
property]
</h2>
<div style="position: relative" class="demo-elements">
<div id="my-anchor" class="anchor">Anchor</div>
<div id="my-target" class="target">Target</div>
</div>
<p class="note">
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).
</p>
<pre><code class="language-css"
>#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);
}</code></pre>
</section>
<section id="custom-prop-passthrough" class="demo-item">
<h2>
<a href="#custom-prop-passthrough" aria-hidden="true">🔗</a>
Positioning with <code>anchor()</code> [passed through multiple CSS
custom properties]
</h2>
<div style="position: relative" class="demo-elements">
<div id="my-anchor-props" class="anchor">Anchor</div>
<div id="my-target-props" class="target">Target</div>
</div>
<p class="note">
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.
</p>
<pre><code class="language-css"
>#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);
}</code></pre>
</section>
<section id="duplicate-custom-props" class="demo-item">
<h2>
<a href="#duplicate-custom-props" aria-hidden="true">🔗</a>
Positioning with <code>anchor()</code> [with duplicate CSS custom
properties]
</h2>
<div style="position: relative" class="demo-elements">
<div id="anchor-duplicate-custom-props" class="anchor">Anchor</div>
<div id="target-duplicate-custom-props" class="target">Target</div>
</div>
<p class="note">
With polyfill applied: Target's top left corner is positioned in the
center (vertically and horizontally) of the Anchor.
</p>
<pre><code class="language-css"
>#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%);
}</code></pre>
</section>
<section id="anchor-size" class="demo-item">
<h2>
<a href="#anchor-size" aria-hidden="true">🔗</a>
Sizing with <code>anchor-size()</code>
</h2>
<div style="position: relative" class="demo-elements">
<div id="my-anchor-size" class="anchor">Anchor</div>
<div id="my-target-size" class="target">Target</div>
</div>
<p class="note">
With polyfill applied: Target has the same width as the Anchor.
</p>
<pre><code class="language-css"
>#my-anchor-size {
anchor-name: --my-anchor;
width: 5em;
}
#my-target-size {
width: anchor-size(--my-anchor width);
}</code></pre>
</section>
<section id="anchor-update" class="demo-item">
<h2>
<a href="#anchor-update" aria-hidden="true">🔗</a>
Dynamically update anchors
</h2>
<div style="position: relative" class="demo-elements">
<div id="my-anchor-update" class="anchor">Anchor</div>
<div id="my-target-update" class="target">Target</div>
</div>
<button id="toggle-anchor-width">Toggle anchor width</button>
<p class="note">
With polyfill applied: Target and Anchor's right edges line up. Target's
top edge lines up with the bottom edge of the Anchor.
<br />
<br />
When Anchor width is changed dynamically, Target position updates
accordingly.
</p>
<pre><code class="language-css"
>#my-anchor-update {