From b25bc3d0b656ae56fdd9277af12c1cb60017267a Mon Sep 17 00:00:00 2001
From: Masahiro FUJIMOTO <mfujimot@gmail.com>
Date: Tue, 4 Jan 2022 21:58:53 +0900
Subject: ツリー構造擬似クラスを変換準備
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+---
+title: ':first-child'
+slug: 'Web/CSS/:first-child'
+tags:
+  - CSS
+  - Layout
+  - Pseudo-class
+  - Reference
+  - Selector
+  - Web
+translation_of: 'Web/CSS/:first-child'
+---
+<div>{{CSSRef}}</div>
+
+<p><strong><code>:first-child</code></strong> は <a href="/ja/docs/Web/CSS">CSS</a> の<a href="/ja/docs/CSS/Pseudo-classes" title="Pseudo-classes">擬似クラス</a>で、兄弟要素のグループの中で最初の要素を表します。</p>
+
+<pre class="brush: css no-line-numbers notranslate">/* 兄弟要素の中で最初の &lt;p&gt; を
+   すべてを選択 */
+p:first-child {
+  color: lime;
+}</pre>
+
+<div class="note">
+<p><strong>注:</strong> 最初の定義では、親のある要素のみが選択されていました。 Selectors Level 4 の初期に、これは必要なくなりました。</p>
+</div>
+
+<h2 id="Syntax" name="Syntax">構文</h2>
+
+{{csssyntax}}
+
+<h2 id="Examples" name="Examples">例</h2>
+
+<h3 id="Basic_example" name="Basic_example">基本的な例</h3>
+
+<h4 id="HTML">HTML</h4>
+
+<pre class="brush: html notranslate">&lt;div&gt;
+  &lt;p&gt;This text is selected!&lt;/p&gt;
+  &lt;p&gt;This text isn't selected.&lt;/p&gt;
+&lt;/div&gt;
+
+&lt;div&gt;
+  &lt;h2&gt;This text isn't selected: it's not a `p`.&lt;/h2&gt;
+  &lt;p&gt;This text isn't selected.&lt;/p&gt;
+&lt;/div&gt;
+</pre>
+
+<h4 id="CSS">CSS</h4>
+
+<pre class="brush: css notranslate">p:first-child {
+  color: lime;
+  background-color: black;
+  padding: 5px;
+}
+</pre>
+
+<h4 id="Result" name="Result">結果</h4>
+
+<p><span>{{EmbedLiveSample('Basic_example', 500, 200)}}</span></p>
+
+<h3 id="Styling_a_list" name="Styling_a_list">リストのスタイル付け</h3>
+
+<h4 id="HTML_2">HTML</h4>
+
+<pre class="brush: html notranslate">&lt;ul&gt;
+  &lt;li&gt;Item 1&lt;/li&gt;
+  &lt;li&gt;Item 2&lt;/li&gt;
+  &lt;li&gt;Item 3
+    &lt;ul&gt;
+      &lt;li&gt;Item 3.1&lt;/li&gt;
+      &lt;li&gt;Item 3.2&lt;/li&gt;
+      &lt;li&gt;Item 3.3&lt;/li&gt;
+    &lt;/ul&gt;
+  &lt;/li&gt;
+&lt;/ul&gt;</pre>
+
+<h4 id="CSS_2">CSS</h4>
+
+<pre class="brush: css notranslate">ul li {
+  color: blue;
+}
+
+ul li:first-child {
+  color: red;
+  font-weight: bold;
+}</pre>
+
+<h4 id="Result_2" name="Result_2">結果</h4>
+
+<p>{{EmbedLiveSample('Styling_a_list')}}</p>
+
+<h2 id="Specifications" name="Specifications">仕様書</h2>
+
+<table class="standard-table">
+ <thead>
+  <tr>
+   <th scope="col">仕様書</th>
+   <th scope="col">状態</th>
+   <th scope="col">備考</th>
+  </tr>
+ </thead>
+ <tbody>
+  <tr>
+   <td>{{SpecName('CSS4 Selectors', '#first-child-pseudo', ':first-child')}}</td>
+   <td>{{Spec2('CSS4 Selectors')}}</td>
+   <td>選択する要素に親を必要としないようにした。</td>
+  </tr>
+  <tr>
+   <td>{{SpecName('CSS3 Selectors', '#first-child-pseudo', ':first-child')}}</td>
+   <td>{{Spec2('CSS3 Selectors')}}</td>
+   <td>変更なし。</td>
+  </tr>
+  <tr>
+   <td>{{SpecName('CSS2.1', 'selector.html#first-child', ':first-child')}}</td>
+   <td>{{Spec2('CSS2.1')}}</td>
+   <td>初回定義</td>
+  </tr>
+ </tbody>
+</table>
+
+<h2 id="Browser_compatibility" name="Browser_compatibility">ブラウザーの互換性</h2>
+
+<p>{{Compat("css.selectors.first-child")}}</p>
+
+<h2 id="See_also" name="See_also">関連情報</h2>
+
+<ul>
+ <li>{{CSSxRef(":-moz-first-node")}} {{Non-standard_Inline}}</li>
+ <li>{{CSSxRef(":first-of-type")}}</li>
+ <li>{{CSSxRef(":last-child")}}</li>
+ <li>{{CSSxRef(":nth-child", ":nth-child()")}}</li>
+</ul>
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