属性によるセレクター

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As you know from your study of HTML, elements can have attributes that give further detail about the element being marked up. In CSS you can use attribute selectors to target elements with certain attributes. This lesson will show you how to use these very useful selectors.

前提条件:

基本的なコンピューターリテラシー、基本的なソフトウェアがインストールされていること、ファイルの扱い、HTML の基本(HTML 入門)および CSS に関するアイデア(CSS の第一歩)に関する基本的な知識を得ている。

目的: 属性セレクターとは何かと、その使い方を学ぶ。

Presence and value selectors

These selectors enable the selection of an element based on the presence of an attribute alone (例えば、href), or on various different matches against the value of the attribute.

Selector 説明
[attr] a[title] Matches elements with an attribute name of attr — the value in square brackets.
[attr=value] a[href="https://example.com"] Matches elements with an attribute name of attr whose value is exactly value — the string inside the quotes.
[attr~=value] p[class~="special"]

Matches elements with an attribute name of attr whose value is exactly value, or elements with a class attribute containing one or more class names, at least one of which matches value.

Note that in a list of multiple class names the separate classes are whitespace-separated.

[attr|=value] div[lang|="zh"] Matches elements with an attribute name of attr whose value can be exactly value or can begin with value immediately followed by a hyphen.

In the example below you can see these selectors being used.

  • By using li[class] we can match any selector with a class attribute. This matches all but the first list item.
  • li[class="a"] matches a selector with a class of a, but not a selector with a class of a with another space-separated class as part of the value. It selects the second list item.
  • li[class~="a"] will match a class of a but also a value that contains the class of a as part of a whitespace-separated list. It selects the second and third list items.

Substring matching selectors

These selectors allow for more advanced matching of substrings inside the value of your attribute. 例えば、if you had classes of box-warning and box-error and wanted to match everything that started with the string "box-", you could use [class^="box-"] to select them both.

Selector 説明
[attr^=value] li[class^="box-"] Matches elements with an attribute name of attr whose value has the substring value at the start of it.
[attr$=value] li[class$="-box"] Matches elements with an attribute name of attr whose value has the substring value at the end of it.
[attr*= ] li[class*="box"] Matches elements with an attribute name of attr whose value contains at least one occurrence of the substring value anywhere within the string.

The next example shows usage of these selectors:

  • li[class^="a"] matches any attribute value which starts with a, so matches the first two list items.
  • li[class$="a"] matches any attribute value that ends with a, so matches the first and third list item.
  • li[class*="a"] matches any attribute value where a appears anywhere in the string, so it matches all of our list items.

Case-sensitivity

If you want to match attribute values case-insensitively you can use the value i before the closing bracket. This flag tells the browser to match ASCII characters case-insensitively. Without the flag the values will be matched according to the case-sensitivity of the document language — in HTML's case it will be case sensitive.

In the example below, the first selector will match a value that begins with a — it only matches the first list item because the other two list items start with an uppercase A. The second selector uses the case-insensitive flag and so matches all of the list items.

: There is also a newer value s, which will force case-sensitive matching in contexts where matching is normally case-insensitive, however this is less well supported in browsers and isn't very useful in an HTML context.

Try it out

In the live example below, add CSS using attribute selectors to do the following:

  • Target the <a> element with a title attribute and make the border pink (border-color: pink).
  • Target the <a> element with an href attribute that contains the word contact somewhere in its value and make the border orange (border-color: orange).
  • Target the <a> element with an href value starting with https and give it a green border (border-color: green).

: You can take a look at the solution here — but try to figure it out yourself first!

Next steps

Now we are done with attribute selectors, you can continue on to the next article and read about pseudo-class and pseudo-element selectors.

このモジュール

  1. カスケードと継承
  2. CSS セレクター
  3. ボックスモデル
  4. 背景と枠線
  5. テキスト方向の操作
  6. 要素のはみ出し(オーバーフロー)
  7. CSS の値と単位
  8. CSS によるサイズ設定
  9. 画像・メディア・フォーム要素
  10. 表のスタイリング
  11. CSS のデバッグ
  12. CSS の整理