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‎techniques/css/C43.html

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<!DOCTYPE html>
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<html xmlns="http://www.w3.org/1999/xhtml" lang="en">
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<head>
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<title>Using CSS margin and scroll-margin to un-obscure content</title>
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<link rel="stylesheet" type="text/css" href="../../css/editors.css"/>
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</head>
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<body>
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<h1>Using <abbr title="Cascading Style Sheets">CSS</abbr> <code class="language-css">margin</code> and <code class="language-css">scroll-margin</code> to un-obscure content</h1>
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<section id="meta">
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<h2>Metadata</h2>
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<p id="id"></p>
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<p id="technology">CSS</p>
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<p id="type"></p>
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</section>
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<section id="applicability">
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<h2>When to Use</h2>
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<p>All technologies that support CSS.</p>
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</section>
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<section id="description">
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<h2>Description</h2>
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<p>The objective of this technique is to ensure that user interface components (for example: links, buttons, and form fields) that are initially completely obscured by a fixed-position component can still be accessed by users. In this example, this is achieved using the CSS <code class="language-css">margin</code> and <code class="language-css">scroll-margin</code> properties to create space underneath the site footer and allow the link in the footer to scroll into view when it is focused with a keyboard.</p>
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</section>
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<section id="examples">
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<h2>Examples</h2>
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<section class="example">
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<h3>Using CSS margin and scroll-margin to un-obscure content</h3>
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<p>This example shows a situation where there is a fixed-position banner at the bottom of the screen that is covering up the site footer, which contains a link. This type of fixed-position banner is a common design for cookie-consent banners.</p>
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<pre><code>&lt;!doctype html&gt;
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&lt;html lang="en"&gt;
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&lt;head&gt;
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&lt;meta charset="utf-8"&gt;
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&lt;meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no"&gt;
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&lt;title&gt;Using CSS margin and scroll-margin to un-obscure content&lt;/title&gt;
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&lt;style&gt;
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:root{
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font-size:100%;
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box-sizing:border-box;
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--banner-background:hsl(60,80%,90%);
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--banner-border:hsl(0, 0%, 50%);
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--default-focus-indicator:hsl(234, 72%, 42%);
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--fixed-banner-focus-indicator:black;
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}
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*, *::after, *::before{
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box-sizing:inherit;
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}
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body{
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background:white;
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color:black;
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font:1rem/1.5 system-ui, "Segoe UI", Roboto, Helvetica, sans-serif;
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margin:0;
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}
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h1, h2, h3, h4, h5, h6{
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font-weight:500;
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}
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.wrapper{
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display:grid;
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gap:1rem;
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grid-template-columns:repeat(9, 1fr);
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grid-template-rows:8rem auto minmax(10rem, max-content);
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height:100vh;
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}
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.wrapper > *{
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border:1px solid black;
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padding:1rem;
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}
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.wrapper :focus-visible{
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outline:2px solid transparent;
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box-shadow:0 5px 0 0 var(--default-focus-indicator);
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}
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header{
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align-items:center;
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display:flex;
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font-size:1.5rem;
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font-weight:bold;
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grid-column:1 / -1;
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grid-row:1;
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}
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main{
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grid-column:1 / 8;
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}
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aside{
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grid-column:8 / 10;
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}
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footer{
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grid-column:1 / -1;
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}
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@media (max-width:70rem){
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main{
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grid-column:1 / -1;
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}
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aside{
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grid-column:1 / -1;
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}
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}
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.fixed-position-banner{
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background:var(--banner-background);
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border:3px solid var(--banner-border);
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bottom:0;
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height:12rem;
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margin-bottom:1rem;
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padding:1rem;
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position:relative;
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width:calc(100vw - 1rem);
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}
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.fixed-position-banner a{
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outline-color:var(--fixed-banner-focus-indicator);
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}
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.fixed-position-banner h2{
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display:inline-block;
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margin-block-start:0;
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padding:0.25em;
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}
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.fixed-position-banner h2:focus-visible{
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outline:2px solid var(--fixed-banner-focus-indicator);
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}
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@media (min-width:70rem), (min-height:60rem){
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.fixed-position-banner{
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margin-bottom:0;
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position:fixed;
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}
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.banner-open{
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margin-bottom:14rem;
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}
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.banner-open footer a{
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scroll-margin-bottom:15.5rem;
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}
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}
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.close-banner{
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background:hsl(0, 0%, 100%);
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border:1px solid hsl(0, 0%, 50%);
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border-radius:3px;
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cursor:pointer;
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font:inherit;
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margin:0;
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padding:0.33em;
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position:absolute;
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right:1rem;
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top:1rem;
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}
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.close-banner-icon{
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display:block;
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height:1rem;
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stroke:currentColor;
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width:1rem;
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}
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.close-banner:focus-visible{
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outline:2px solid var(--fixed-banner-focus-indicator);
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outline-offset:2px;
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}
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&lt;/style&gt;
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&lt;/head&gt;
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&lt;body&gt;
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&lt;dialog class="fixed-position-banner"&gt;
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&lt;h2 tabindex="-1"&gt;Fixed-Position Banner&lt;/h2&gt;
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&lt;button aria-label="close fixed-position banner" class="close-banner" type="button"&gt;
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&lt;svg aria-hidden="true" class="close-banner-icon" role="img" viewbox="0 0 16 16"&gt;
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&lt;line x1="0" y1="0" x2="15" y2="15" /&gt;
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&lt;line x1="0" y1="15" x2="15" y2="0" /&gt;
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&lt;/svg&gt;
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&lt;/button&gt;
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&lt;/dialog&gt;
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&lt;div class="wrapper"&gt;
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&lt;header&gt;
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&lt;p&gt;Header Content&lt;/p&gt;
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&lt;/header&gt;
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&lt;main&gt;
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&lt;h1&gt;Main Content&lt;/h1&gt;
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&lt;/main&gt;
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&lt;aside&gt;
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&lt;h2&gt;Sidebar Content&lt;/h2&gt;
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&lt;/aside&gt;
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&lt;footer&gt;
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&lt;h2&gt;Footer Content&lt;/h2&gt;
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&lt;p&gt;&lt;a href="https://example.com"&gt;Here&#39;s an example link in the footer&lt;/a&gt;.&lt;/p&gt;
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&lt;/footer&gt;
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&lt;/div&gt;
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&lt;script&gt;
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document.addEventListener(&quot;DOMContentLoaded&quot;, function(e){
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const cookieBanner = document.querySelector(&quot;.fixed-position-banner&quot;);
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const closeBannerBtn = document.querySelector(&quot;.close-banner&quot;);
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const pageBody = document.querySelector(&quot;body&quot;);
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cookieBanner.show();
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if(cookieBanner.hasAttribute(&quot;open&quot;)){
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pageBody.classList.add(&quot;banner-open&quot;);
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}
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closeBannerBtn.addEventListener(&quot;click&quot;, function(e){
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cookieBanner.close();
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pageBody.classList.remove(&quot;banner-open&quot;);
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}, false);
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});
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&lt;/script&gt;
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&lt;/body&gt;
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&lt;/html&gt;</code></pre>
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<aside class="note">
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<p>Due to the current lack of cross-browser support for the the CSS <code class="language-css">:has</code> pseudo-class, this example uses JavaScript to create the <code class="language-css">margin</code> at the bottom of the page. Using the <code class="language-css">:has</code> selector, the relevant CSS is:</p>
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<pre><code>body:has(.fixed-position-banner[open]){
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margin-bottom:14rem;
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}
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body:has(.fixed-position-banner[open]) footer a{
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scroll-margin-bottom:15.5rem;
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}</code></pre>
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</aside>
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</section>
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</section>
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<section id="tests">
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<h2>Tests</h2>
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<section class="test-procedure">
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<h3>Procedure</h3>
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<p>For each user interface component that entirely hidden by author-created content and receives keyboard focus:</p>
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<ol>
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<li>Check that the user interface component becomes not entirely hidden when it receives keyboard focus.</li>
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</ol>
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</section>
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<section class="test-results">
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<h3>Expected Results</h3>
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<ul>
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<li>Check 1 is true.</li>
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</ul>
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</section>
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</section>
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<section id="related">
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<h2>Related Techniques</h2>
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<ol>
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<li><a href="C32">C32</a></li>
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<li><a href="C34">C34</a></li>
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</ol>
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</section>
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<section id="resources">
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<h2>Resources</h2>
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<ol>
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<li><a href="https://www.w3.org/TR/css-box/#margins"><abbr title="World Wide Web Consortium">W3C</abbr> - CSS margins</a></li>
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<li><a href="https://www.w3.org/TR/css-scroll-snap/#scroll-margin">W3C - CSS the <code class="language-css">scroll-margin</code> property</a>.</li>
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<li><a href="https://developer.mozilla.org/en-US/docs/Web/CSS/:has"><abbr title="Mozilla Developer Network">MDN</abbr> - <code class="language-css">:has()</code> property</a>.</li>
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</ol>
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</section>
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</body>
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</html>

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