<p><img src="/static/imghw/default1.png" data-src="https://img.php.cn/upload/article/000/000/000/174010351218537.jpg" class="lazy" alt="The PostCSS Guide to Improving Selectors and Media Queries "></p> <p><strong>Core points</strong></p> <ul> <li>PostCSS provides a variety of plugins that provide polyfills for the latest CSS features, allowing developers to try out new features even if they lack extensive browser support. </li> <li> <code>postcss-nesting</code> The plug-in implements style rules nesting according to the W3C nested module proposal, introducing a new <code>&amp;amp;amp;</code> nested selector, referring to the parent selector. </li> <li> <code>postcss-custom-selectors</code> Plugin allows defining duplication selectors in variables, reducing code duplication and improving code maintenance. </li> The <li> <code>postcss-custom-media</code> and <code>postcss-media-minmax</code> plugins improve media queries to make them easier to use and reduce duplication in style sheets. </li> </ul> <p>The latest changes to the CSS specification introduce some interesting features. Unfortunately, some of these features are still in the draft stage, while others lack extensive browser support. Often, new suggestions take some time before they are reviewed, accepted and implemented by the browser. However, we can save waiting time and try some of these features using PostCSS. </p> <p>PostCSS has various plug-ins designed to implement polyfills for the latest CSS features. Because these plugins are very wide, it is difficult to cover all plugins in one article. Instead, we will focus on plugins that focus on adding new features to selectors and media queries. Many plugins will allow us to significantly improve the structure of the stylesheet, while others may just add some clean syntactic sugar to the top. </p> <p>This article will not introduce the configuration and installation of PostCSS in detail. This has been described in "Begin with PostCSS" and "Improving CSS Quality with PostCSS". As a quick reference, you can also check out the PostCSS page on GitHub. </p> <h2 id="Rules-nesting">Rules nesting</h2> <p>Let's start with the most basic functionality—certainly familiar to every preprocessor user—Nesting. <code>postcss-nesting</code> Plug-in implements style rules nesting according to W3C nested module proposals. </p> <p>The proposal introduces a new <code>&amp;amp;amp;</code> nested selector that references the parent selector. Contrary to Less or Sass, this selector is required by specification and must be the first basic selector in the selector chain to enable nesting. Any selector that does not contain nested selectors will be ignored. For example: </p> <pre class='brush:php;toolbar:false;'>.article { color: #333; &amp;amp;amp;amp;.popular { background: #DDD; } &amp;amp;amp;amp; .title { font-weight: bold; } }</pre> <p> will be converted to: </p> <pre class='brush:php;toolbar:false;'>.article { color: #333 } .article.popular { background: #DDD } .article .title { font-weight: bold }</pre> <p> Please note that the following code is invalid because it does not use the <code>&amp;amp;amp;</code> selector as specified. </p> <pre class='brush:php;toolbar:false;'>.article { color: #333; /* no nested-selector */ .popular { background: #DDD; } /* the nested selector is not the fist selector in the chain */ .latest &amp;amp;amp;amp;amp; { border: 1px solid red; } }</pre> <p> To allow the parent selector to be inserted anywhere in the selector (not just at the beginning), the proposal defines an alternative syntax to use nested at-rule <code>@nest</code> . We can fix the <code>.latest &amp;amp;amp;amp;</code> selector in the previous example by: </p> <pre class='brush:php;toolbar:false;'>.article { color: #333; @nest .latest &amp;amp;amp;amp;amp; { border: 1px solid red; } }</pre> <p>This will compile to: </p> <pre class='brush:php;toolbar:false;'>.article { color: #333 } .latest .article { border: 1px solid red }</pre> <p><code>@nest</code> The grammar is also more expressive than <code>&amp;amp;amp;</code>. </p><h2 id="Custom-selector">Custom selector</h2> <p>When writing CSS, we tend to write many duplicate selectors. This could be a simple boilerplate code that selects all links or any buttons, or a more complex selector that requires repeated repetitions. This may introduce many code duplications and all related code maintenance issues. The new CSS extension specification introduces a way to store selectors in variables and reference them from other parts of the stylesheet. Therefore, a repeat selector needs to be defined only once and then it can be safely reused elsewhere. </p> <p>PostCSS has a <code>postcss-custom-selectors</code> plugin that implements this feature. Here is a simple example that defines all title element selectors: </p> <pre class='brush:php;toolbar:false;'>.article { color: #333; &amp;amp;amp;amp;.popular { background: #DDD; } &amp;amp;amp;amp; .title { font-weight: bold; } }</pre> <p>It will compile to: </p> <pre class='brush:php;toolbar:false;'>.article { color: #333 } .article.popular { background: #DDD } .article .title { font-weight: bold }</pre> <p>Custom selectors are implemented as pseudo-classes, so the syntax looks weird <code>:--</code>. </p> <p>Custom selectors can be used effectively with basic selectors. For example: </p> <pre class='brush:php;toolbar:false;'>.article { color: #333; /* no nested-selector */ .popular { background: #DDD; } /* the nested selector is not the fist selector in the chain */ .latest &amp;amp;amp;amp;amp; { border: 1px solid red; } }</pre> <p>Compiled to: </p> <pre class='brush:php;toolbar:false;'>.article { color: #333; @nest .latest &amp;amp;amp;amp;amp; { border: 1px solid red; } }</pre> <p>You can even combine multiple custom selectors into a single selector for more complex arrangements. </p> <pre class='brush:php;toolbar:false;'>.article { color: #333 } .latest .article { border: 1px solid red }</pre> <p> Will generate: </p> <pre class='brush:php;toolbar:false;'>@custom-selector :--heading h1, h2, h3, h4, h5, h6; :--heading { font-weight: bold; }</pre> <p>This example may be a little overblown, but it demonstrates the power of this feature very well. </p> <h2 id="New-pseudo-class">New pseudo-class</h2> The selector level 4 specification introduces a bunch of new pseudo-classes, but due to the dynamic nature of most pseudo-classes, only a few are available as PostCSS plug-ins. <p> </p><h3> Pseudoclass<code>:matches()</code> The </h3><p> plugin implements a new <code>postcss-selector-matches</code> pseudo-class. It is a function class that filters only elements that match the selector in the parameter. If you pass multiple selectors, the elements must match at least one of them. In short: <code>:matches()</code> </p> <pre class='brush:php;toolbar:false;'>h1, h2, h3, h4, h5, h6 { font-weight: bold; }</pre>Compiled to: <p> </p> <pre class='brush:php;toolbar:false;'>.article :--heading .author { color: blue; }</pre><h3> Pseudoclass<code>:not()</code> </h3><p> Pseudo-class filtering elements that do not match any given parameter. It is implemented in the <code>:not()</code> plugin. <code>postcss-selector-not</code> </p> <pre class='brush:php;toolbar:false;'>.article h1 .author, .article h2 .author, .article h3 .author, .article h4 .author, .article h5 .author, .article h6 .author { color: blue; }</pre>The result is: <p> </p> <pre class='brush:php;toolbar:false;'>@custom-selector :--links a, a:focus, a:visited, a:hover, a:active; article :--heading :--links { color: #333; }</pre><h3> Pseudoclass<code>:any-link</code> </h3><p> plugin implements the <code>postcss-pseudo-class-any-link</code> pseudo-class. It was introduced to help resolve confusion around the <code>:any-link</code> pseudo-class. Unlike the latter, it matches all links – including those visited. <code>:link</code> </p> <pre class='brush:php;toolbar:false;'>article h1 a, article h2 a, article h3 a, article h4 a, article h5 a, article h6 a, article h1 a:focus, article h2 a:focus, article h3 a:focus, article h4 a:focus, article h5 a:focus, article h6 a:focus, article h1 a:visited, article h2 a:visited, article h3 a:visited, article h4 a:visited, article h5 a:visited, article h6 a:visited, article h1 a:hover, article h2 a:hover, article h3 a:hover, article h4 a:hover, article h5 a:hover, article h6 a:hover, article h1 a:active, article h2 a:active, article h3 a:active, article h4 a:active, article h5 a:active, article h6 a:active { color: #333; }</pre>Compiled to: <p> </p> <pre class='brush:php;toolbar:false;'>button:matches(:hover, :focus) { color: red; }</pre>Media Query Improvement<h2> </h2>There are plugins in the library for PostCSS to make media queries easier to use. They are <p> and <code>postcss-custom-media</code>. <code>postcss-media-minmax</code> </p>Custom Media<h3> </h3>Writing media queries creates the same problems as regular selectors - they are often repeated in style sheets. Probably more frequent than normal selectors. Fortunately, there is a solution similar to a custom selector. <p> The plug-in implements a custom media query specification that increases the ability to save media queries into variables. <code>postcss-custom-media</code> </p>The syntax is very similar to a custom selector. Here is a simple example: <p> </p> <pre class='brush:php;toolbar:false;'>button:hover, button:focus { color: red; }</pre>Compiled to: <p><pre class='brush:php;toolbar:false;'>.article { color: #333; &amp;amp;amp;amp;.popular { background: #DDD; } &amp;amp;amp;amp; .title { font-weight: bold; } }</pre> <p> Of course, you can use multiple custom media queries at once: </p> <pre class='brush:php;toolbar:false;'>.article { color: #333 } .article.popular { background: #DDD } .article .title { font-weight: bold }</pre> <p> Will generate: </p> <pre class='brush:php;toolbar:false;'>.article { color: #333; /* no nested-selector */ .popular { background: #DDD; } /* the nested selector is not the fist selector in the chain */ .latest &amp;amp;amp;amp;amp; { border: 1px solid red; } }</pre> <p>As you can see, it is now much easier to change the definition of "medium viewport" and find any relevant CSS code. </p> <h3 id="Minimum-and-Maximum-Syntax">Minimum and Maximum Syntax</h3> <p> Although media queries are a great thing, the minimum and maximum grammars have received a lot of criticism from the community. W3C responds by introducing a more intuitive syntax using comparison operators. <code>postcss-media-minmax</code> Plugin adds support for <code>></code>, <code>>=</code>, <code><</code>, <code><=</code>, </p>. <p> </p>(The rest of the article has been omitted due to the length of the article, but the image link remains unchanged)

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