davidbgk
/
larlet-fr-david-cache


			
							123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300301302303304305306307308309310311312
							<!doctype html><!-- This is a valid HTML5 document. -->
<!-- Screen readers, SEO, extensions and so on. -->
<html lang="en">
<!-- Has to be within the first 1024 bytes, hence before the `title` element
  See: https://www.w3.org/TR/2012/CR-html5-20121217/document-metadata.html#charset -->
<meta charset="utf-8">
<!-- Why no `X-UA-Compatible` meta: https://stackoverflow.com/a/6771584 -->
<!-- The viewport meta is quite crowded and we are responsible for that.
  See: https://codepen.io/tigt/post/meta-viewport-for-2015 -->
<meta name="viewport" content="width=device-width,initial-scale=1">
<!-- Required to make a valid HTML5 document. -->
<title>An advanced way to use CSS variables (archive) — David Larlet</title>
<meta name="description" content="Publication mise en cache pour en conserver une trace.">
<!-- That good ol' feed, subscribe :). -->
<link rel="alternate" type="application/atom+xml" title="Feed" href="/david/log/">
<!-- Generated from https://realfavicongenerator.net/ such a mess. -->
<link rel="apple-touch-icon" sizes="180x180" href="/static/david/icons2/apple-touch-icon.png">
<link rel="icon" type="image/png" sizes="32x32" href="/static/david/icons2/favicon-32x32.png">
<link rel="icon" type="image/png" sizes="16x16" href="/static/david/icons2/favicon-16x16.png">
<link rel="manifest" href="/static/david/icons2/site.webmanifest">
<link rel="mask-icon" href="/static/david/icons2/safari-pinned-tab.svg" color="#07486c">
<link rel="shortcut icon" href="/static/david/icons2/favicon.ico">
<meta name="msapplication-TileColor" content="#f7f7f7">
<meta name="msapplication-config" content="/static/david/icons2/browserconfig.xml">
<meta name="theme-color" content="#f7f7f7" media="(prefers-color-scheme: light)">
<meta name="theme-color" content="#272727" media="(prefers-color-scheme: dark)">
<!-- Is that even respected? Retrospectively? What a shAItshow…
  https://neil-clarke.com/block-the-bots-that-feed-ai-models-by-scraping-your-website/ -->
<meta name="robots" content="noai, noimageai">
<!-- Documented, feel free to shoot an email. -->
<link rel="stylesheet" href="/static/david/css/style_2021-01-20.css">
<!-- See https://www.zachleat.com/web/comprehensive-webfonts/ for the trade-off. -->
<link rel="preload" href="/static/david/css/fonts/triplicate_t4_poly_regular.woff2" as="font" type="font/woff2" media="(prefers-color-scheme: light), (prefers-color-scheme: no-preference)" crossorigin>
<link rel="preload" href="/static/david/css/fonts/triplicate_t4_poly_bold.woff2" as="font" type="font/woff2" media="(prefers-color-scheme: light), (prefers-color-scheme: no-preference)" crossorigin>
<link rel="preload" href="/static/david/css/fonts/triplicate_t4_poly_italic.woff2" as="font" type="font/woff2" media="(prefers-color-scheme: light), (prefers-color-scheme: no-preference)" crossorigin>
<link rel="preload" href="/static/david/css/fonts/triplicate_t3_regular.woff2" as="font" type="font/woff2" media="(prefers-color-scheme: dark)" crossorigin>
<link rel="preload" href="/static/david/css/fonts/triplicate_t3_bold.woff2" as="font" type="font/woff2" media="(prefers-color-scheme: dark)" crossorigin>
<link rel="preload" href="/static/david/css/fonts/triplicate_t3_italic.woff2" as="font" type="font/woff2" media="(prefers-color-scheme: dark)" crossorigin>
<script>
    function toggleTheme(themeName) {
        document.documentElement.classList.toggle(
            'forced-dark',
            themeName === 'dark'
        )
        document.documentElement.classList.toggle(
            'forced-light',
            themeName === 'light'
        )
    }
    const selectedTheme = localStorage.getItem('theme')
    if (selectedTheme !== 'undefined') {
        toggleTheme(selectedTheme)
    }
</script>

  <meta name="robots" content="noindex, nofollow">
  <meta content="origin-when-cross-origin" name="referrer">
  <!-- Canonical URL for SEO purposes -->
  <link rel="canonical" href="https://gomakethings.com/an-advanced-way-to-use-css-variables/">

<body class="remarkdown h1-underline h2-underline h3-underline em-underscore hr-center ul-star pre-tick" data-instant-intensity="viewport-all">


<article>
  <header>
    <h1>An advanced way to use CSS variables</h1>
  </header>
  <nav>
    <p class="center">
      <a href="/david/" title="Aller à l’accueil"><svg class="icon icon-home">
        <use xlink:href="/static/david/icons2/symbol-defs-2021-12.svg#icon-home"></use>
      </svg> Accueil</a> •
      <a href="https://gomakethings.com/an-advanced-way-to-use-css-variables/" title="Lien vers le contenu original">Source originale</a>
      <br>
      Mis en cache le 2024-04-08
    </p>
  </nav>
  <hr>
  <p>Let’s dig in!</p>

<h2 id="globals-for-system-or-theme-defaults">Globals for system or theme defaults</h2>

<p>I like to scope design system or theme defaults to the <code>:root</code> element. This makes them accessible to every element and class in the design system.</p>
<div class="highlight"><pre class="chroma"><code class="language-css" data-lang="css"><span class="p">:</span><span class="nd">root</span> <span class="p">{</span>

<span class="c">/_ Colors _/</span>
<span class="nv">--color-primary</span><span class="p">:</span> <span class="mh">#0088cc</span><span class="p">;</span>
<span class="nv">--color-secondary</span><span class="p">:</span> <span class="kc">rebeccapurple</span><span class="p">;</span>
<span class="nv">--color-black</span><span class="p">:</span> <span class="mh">#272727</span><span class="p">;</span>
<span class="nv">--color-white</span><span class="p">:</span> <span class="mh">#ffffff</span><span class="p">;</span>

<span class="c">/_ Sizes _/</span>
<span class="nv">--size-default</span><span class="p">:</span> <span class="mi">1</span><span class="kt">rem</span><span class="p">;</span>
<span class="nv">--size-small</span><span class="p">:</span> <span class="mf">0.875</span><span class="kt">rem</span><span class="p">;</span>
<span class="nv">--size-large</span><span class="p">:</span> <span class="mf">1.25</span><span class="kt">rem</span><span class="p">;</span>

<span class="c">/_ Typefaces _/</span>
<span class="nv">--font-sans</span><span class="p">:</span> <span class="s2">"PT Sans"</span><span class="p">,</span> <span class="n">sans</span><span class="p">;</span>
<span class="nv">--font-serif</span><span class="p">:</span> <span class="s2">"PT Serif"</span><span class="p">,</span> <span class="kc">serif</span><span class="p">;</span>
<span class="nv">--font-mono</span><span class="p">:</span> <span class="n">Menlo</span><span class="p">,</span> <span class="n">Monaco</span><span class="p">,</span> <span class="s2">"Courier New"</span><span class="p">,</span> <span class="kc">monospace</span><span class="p">;</span>

<span class="p">}</span></code></pre></div>

<p>I typically have variables for <code>--color-*</code>, <code>--size-*</code>, and <code>--font-*</code>, as well as ones to define the max width of containers and how much <code>--spacing</code> to use between paragraphs and various elements.</p>

<h2 id="styling-elements">Styling elements</h2>

<p>Let’s look at styles for a <code>button</code> element.</p>
<div class="highlight"><pre class="chroma"><code class="language-css" data-lang="css"><span class="nt">button</span> <span class="p">{</span>
<span class="k">background-color</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="kc">color</span><span class="o">-</span><span class="n">primary</span><span class="p">);</span>
<span class="k">border</span><span class="p">:</span> <span class="mf">0.125</span><span class="kt">rem</span> <span class="kc">solid</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="kc">color</span><span class="o">-</span><span class="n">primary</span><span class="p">);</span>
<span class="k">border-radius</span><span class="p">:</span> <span class="mf">0.25</span><span class="kt">em</span><span class="p">;</span>
<span class="k">color</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="kc">color</span><span class="o">-</span><span class="kc">white</span><span class="p">);</span>
<span class="k">display</span><span class="p">:</span> <span class="kc">inline</span><span class="o">-</span><span class="kc">block</span><span class="p">;</span>
<span class="k">font-size</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="n">font</span><span class="o">-</span><span class="kc">default</span><span class="p">);</span>
<span class="k">font-weight</span><span class="p">:</span> <span class="kc">normal</span><span class="p">;</span>
<span class="k">line-height</span><span class="p">:</span> <span class="mf">1.2</span><span class="p">;</span>
<span class="k">padding</span><span class="p">:</span> <span class="mf">0.5</span><span class="kt">rem</span> <span class="mf">0.6875</span><span class="kt">rem</span><span class="p">;</span>
<span class="p">}</span>

<span class="nt">button</span><span class="p">:</span><span class="nd">hover</span> <span class="p">{</span>
<span class="k">background-color</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="kc">color</span><span class="o">-</span><span class="n">secondary</span><span class="p">);</span>
<span class="k">border-color</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="kc">color</span><span class="o">-</span><span class="n">secondary</span><span class="p">);</span>
<span class="p">}</span></code></pre></div>

<p>Let’s say we want to add a secondary button style: the <code>.btn-secondary</code> class.</p>
<div class="highlight"><pre class="chroma"><code class="language-html" data-lang="html"><span class="p">&lt;</span><span class="nt">button</span><span class="p">&gt;</span>Primary Button<span class="p">&lt;/</span><span class="nt">button</span><span class="p">&gt;</span>
<span class="p">&lt;</span><span class="nt">button</span> <span class="na">class</span><span class="o">=</span><span class="s">"btn-secondary"</span><span class="p">&gt;</span>Secondary Button<span class="p">&lt;/</span><span class="nt">button</span><span class="p">&gt;</span></code></pre></div>
<p>Using only globals, we might write the CSS like this.</p>
<div class="highlight"><pre class="chroma"><code class="language-css" data-lang="css"><span class="p">.</span><span class="nc">btn-secondary</span> <span class="p">{</span>
<span class="k">background-color</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="kc">color</span><span class="o">-</span><span class="n">secondary</span><span class="p">);</span>
<span class="k">border-color</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="kc">color</span><span class="o">-</span><span class="n">secondary</span><span class="p">);</span>
<span class="p">}</span>

<span class="p">.</span><span class="nc">btn-secondary</span><span class="p">:</span><span class="nd">hover</span> <span class="p">{</span>
<span class="k">background-color</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="kc">color</span><span class="o">-</span><span class="n">primary</span><span class="p">);</span>
<span class="k">border-color</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="kc">color</span><span class="o">-</span><span class="n">primary</span><span class="p">);</span>
<span class="p">}</span></code></pre></div>

<p>It totally works, and we can easily update our global colors later and have them automatically update the button styles.</p>

<p>But there’s another way we could approach this that I think works a <em>little</em> bit better.</p>

<h2 id="css-variables-scoped-to-the-element">CSS variables scoped to the element</h2>

<p>While global variables scoped to the <code>:root</code> let me define system-wide defaults, I also like to scope variables for <a href="https://gomakethings.com/hug-css-how-i-approach-css-architecture/">styles that change with utility classes</a> to the element itself.</p>

<p>CSS variables scoped to an element can use other CSS variables as their value. But scoping them to the element provides an easy way to modify them.</p>

<p>Looking at our <code>button</code> again, I’ll often do something like this…</p>
<div class="highlight"><pre class="chroma"><code class="language-css" data-lang="css"><span class="nt">button</span> <span class="p">{</span>
<span class="nv">--bg-color</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="kc">color</span><span class="o">-</span><span class="n">primary</span><span class="p">);</span>
<span class="nv">--color</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="kc">color</span><span class="o">-</span><span class="kc">white</span><span class="p">);</span>
<span class="nv">--size</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="n">font</span><span class="o">-</span><span class="kc">default</span><span class="p">);</span>
<span class="nv">--padding-x</span><span class="p">:</span> <span class="mf">0.6875</span><span class="kt">rem</span><span class="p">;</span>
<span class="nv">--padding-y</span><span class="p">:</span> <span class="mf">0.5</span><span class="kt">rem</span><span class="p">;</span>

<span class="k">background-color</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="n">bg</span><span class="o">-</span><span class="kc">color</span><span class="p">);</span>
<span class="k">border</span><span class="p">:</span> <span class="mf">0.125</span><span class="kt">rem</span> <span class="kc">solid</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="n">bg</span><span class="o">-</span><span class="kc">color</span><span class="p">);</span>
<span class="k">border-radius</span><span class="p">:</span> <span class="mf">0.25</span><span class="kt">em</span><span class="p">;</span>
<span class="k">color</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="kc">color</span><span class="p">);</span>
<span class="k">display</span><span class="p">:</span> <span class="kc">inline</span><span class="o">-</span><span class="kc">block</span><span class="p">;</span>
<span class="k">font-size</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="n">size</span><span class="p">);</span>
<span class="k">font-weight</span><span class="p">:</span> <span class="kc">normal</span><span class="p">;</span>
<span class="k">line-height</span><span class="p">:</span> <span class="mf">1.2</span><span class="p">;</span>
<span class="k">padding</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="n">padding</span><span class="o">-</span><span class="n">y</span><span class="p">)</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="n">padding</span><span class="o">-</span><span class="n">x</span><span class="p">);</span>
<span class="p">}</span></code></pre></div>

<p>Now, to change the <code>button:hover</code> style, I only need to update the <code>--bg-color</code> variable, which controls both the <code>background-color</code> and <code>border-color</code> properties.</p>
<div class="highlight"><pre class="chroma"><code class="language-css" data-lang="css"><span class="nt">button</span><span class="p">:</span><span class="nd">hover</span> <span class="p">{</span>
<span class="nv">--bg-color</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="kc">color</span><span class="o">-</span><span class="n">secondary</span><span class="p">);</span>
<span class="p">}</span></code></pre></div>
<p><a href="https://codepen.io/cferdinandi/pen/gOyovdE">Here’s a demo.</a></p>

<h2 id="a-growing-system">A growing system</h2>

<p>This approach is a little bit more work up-front, but it has bigger payoffs the more you use it.</p>

<p>For example, our <code>.btn-secondary</code> class gets shorter.</p>
<div class="highlight"><pre class="chroma"><code class="language-css" data-lang="css"><span class="p">.</span><span class="nc">btn-secondary</span> <span class="p">{</span>
<span class="nv">--bg-color</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="kc">color</span><span class="o">-</span><span class="n">secondary</span><span class="p">);</span>
<span class="p">}</span>

<span class="p">.</span><span class="nc">btn-secondary</span><span class="p">:</span><span class="nd">hover</span> <span class="p">{</span>
<span class="nv">--bg-color</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="kc">color</span><span class="o">-</span><span class="n">primary</span><span class="p">);</span>
<span class="p">}</span></code></pre></div>

<p>With every utility class you add to modify your base styles, using element-scoped CSS variables makes things a bit easier.</p>

<p>For example, we can add <code>.btn-large</code> and <code>.btn-small</code> classes by doing this…</p>
<div class="highlight"><pre class="chroma"><code class="language-css" data-lang="css"><span class="p">.</span><span class="nc">btn-large</span> <span class="p">{</span>
<span class="nv">--size</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="n">font</span><span class="o">-</span><span class="kc">large</span><span class="p">);</span>
<span class="nv">--padding-x</span><span class="p">:</span> <span class="mf">0.875</span><span class="kt">rem</span><span class="p">;</span>
<span class="nv">--padding-y</span><span class="p">:</span> <span class="mf">0.75</span><span class="kt">rem</span><span class="p">;</span>
<span class="p">}</span>

<span class="p">.</span><span class="nc">btn-small</span> <span class="p">{</span>
<span class="nv">--size</span><span class="p">:</span> <span class="nf">var</span><span class="p">(</span><span class="o">--</span><span class="n">font</span><span class="o">-</span><span class="kc">small</span><span class="p">);</span>
<span class="nv">--padding-x</span><span class="p">:</span> <span class="mf">0.5</span><span class="kt">rem</span><span class="p">;</span>
<span class="nv">--padding-y</span><span class="p">:</span> <span class="mf">0.25</span><span class="kt">rem</span><span class="p">;</span>
<span class="p">}</span></code></pre></div>

<p><a href="https://codepen.io/cferdinandi/pen/vYMpdVV">Here’s another demo.</a></p>

<h2 id="should-you-always-do-this">Should you always do this?</h2>

<p>Nope! It’s a lot more work, and sometimes results in code that’s a bit less readable at first glance.</p>

<p>It’s a good approach to use…</p>

<ul>
<li>For properties that will change through modifier or utility classes.</li>
<li>For design systems where end-users will need to easily override certain styles in ways you can’t predict.</li>
</ul>
</article>


<hr>

<footer>
  <p>
    <a href="/david/" title="Aller à l’accueil"><svg class="icon icon-home">
        <use xlink:href="/static/david/icons2/symbol-defs-2021-12.svg#icon-home"></use>
      </svg> Accueil</a> •
    <a href="/david/log/" title="Accès au flux RSS"><svg class="icon icon-rss2">
        <use xlink:href="/static/david/icons2/symbol-defs-2021-12.svg#icon-rss2"></use>
      </svg> Suivre</a> •
    <a href="http://larlet.com" title="Go to my English profile" data-instant><svg class="icon icon-user-tie">
        <use xlink:href="/static/david/icons2/symbol-defs-2021-12.svg#icon-user-tie"></use>
      </svg> Pro</a> •
    <a href="mailto:david%40larlet.fr" title="Envoyer un courriel"><svg class="icon icon-mail">
        <use xlink:href="/static/david/icons2/symbol-defs-2021-12.svg#icon-mail"></use>
      </svg> Email</a> •
    <abbr class="nowrap" title="Hébergeur : Alwaysdata, 62 rue Tiquetonne 75002 Paris, +33184162340"><svg class="icon icon-hammer2">
        <use xlink:href="/static/david/icons2/symbol-defs-2021-12.svg#icon-hammer2"></use>
      </svg> Légal</abbr>
  </p>
  <template id="theme-selector">
      <form>
          <fieldset>
              <legend><svg class="icon icon-brightness-contrast">
                <use xlink:href="/static/david/icons2/symbol-defs-2021-12.svg#icon-brightness-contrast"></use>
              </svg> Thème</legend>
              <label>
                  <input type="radio" value="auto" name="chosen-color-scheme" checked> Auto
              </label>
              <label>
                  <input type="radio" value="dark" name="chosen-color-scheme"> Foncé
              </label>
              <label>
                  <input type="radio" value="light" name="chosen-color-scheme"> Clair
              </label>
          </fieldset>
      </form>
  </template>
</footer>
<script src="/static/david/js/instantpage-5.1.0.min.js" type="module"></script>
<script>
    function loadThemeForm(templateName) {
        const themeSelectorTemplate = document.querySelector(templateName)
        const form = themeSelectorTemplate.content.firstElementChild
        themeSelectorTemplate.replaceWith(form)

        form.addEventListener('change', (e) => {
            const chosenColorScheme = e.target.value
            localStorage.setItem('theme', chosenColorScheme)
            toggleTheme(chosenColorScheme)
        })

        const selectedTheme = localStorage.getItem('theme')
        if (selectedTheme && selectedTheme !== 'undefined') {
            form.querySelector(`[value="${selectedTheme}"]`).checked = true
        }
    }

    const prefersColorSchemeDark = '(prefers-color-scheme: dark)'
    window.addEventListener('load', () => {
        let hasDarkRules = false
        for (const styleSheet of Array.from(document.styleSheets)) {
            let mediaRules = []
            for (const cssRule of styleSheet.cssRules) {
                if (cssRule.type !== CSSRule.MEDIA_RULE) {
                    continue
                }
                // WARNING: Safari does not have/supports `conditionText`.
                if (cssRule.conditionText) {
                    if (cssRule.conditionText !== prefersColorSchemeDark) {
                        continue
                    }
                } else {
                    if (cssRule.cssText.startsWith(prefersColorSchemeDark)) {
                        continue
                    }
                }
                mediaRules = mediaRules.concat(Array.from(cssRule.cssRules))
            }

            // WARNING: do not try to insert a Rule to a styleSheet you are
            // currently iterating on, otherwise the browser will be stuck
            // in a infinite loop…
            for (const mediaRule of mediaRules) {
                styleSheet.insertRule(mediaRule.cssText)
                hasDarkRules = true
            }
        }
        if (hasDarkRules) {
            loadThemeForm('#theme-selector')
        }
    })
</script>
</body>
</html>