143 lines
3.7 KiB
Markdown
143 lines
3.7 KiB
Markdown
---
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id: bad87fee1348bd9aecf08806
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title: 使用 class 选择器设置单个元素的样式
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challengeType: 0
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videoUrl: 'https://scrimba.com/c/c2MvDtV'
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forumTopicId: 18337
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dashedName: use-a-css-class-to-style-an-element
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---
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# --description--
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CSS 的 class 具有可重用性，可应用于各种 HTML 元素。
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一个 CSS class 声明示例如下所示：
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```html
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<style>
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.blue-text {
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color: blue;
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}
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</style>
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```
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可以看到，我们在 `<style>` 样式声明区域里，创建了一个名为 `blue-text` 的 `class` 选择器。 你可以这样将 class 应用于 HTML 元素：`<h2 class="blue-text">CatPhotoApp</h2>`。 注意在 CSS `style` 元素里，class 名以一个句点开头。 在 HTML 元素的 class 属性中，class 名的开头没有句点。
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# --instructions--
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在 `style` 样式声明里，把 `h2` 元素选择器改为 `.red-text` class 选择器，同时将颜色 `blue` 改为 `red`。
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给 `h2` 元素设置一个值为 `red-text` 的 `class` 属性。
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# --hints--
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`h2` 元素应为红色。
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```js
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assert($('h2').css('color') === 'rgb(255, 0, 0)');
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```
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`h2` 元素应有一个 `red-text` class。
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```js
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assert($('h2').hasClass('red-text'));
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```
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样式表应该声明一个 `red-text` class，颜色为 `red`。
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```js
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assert(code.match(/\.red-text\s*\{\s*color\s*:\s*red;?\s*\}/g));
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```
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不应在 `h2` 元素里使用行内样式 `style="color: red"`。
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```js
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assert($('h2').attr('style') === undefined);
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```
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# --seed--
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## --seed-contents--
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```html
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<style>
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h2 {
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color: blue;
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}
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</style>
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<h2>CatPhotoApp</h2>
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<main>
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<p>Click here to view more <a href="#">cat photos</a>.</p>
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<a href="#"><img src="https://cdn.freecodecamp.org/curriculum/cat-photo-app/relaxing-cat.jpg" alt="A cute orange cat lying on its back."></a>
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<div>
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<p>Things cats love:</p>
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<ul>
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<li>cat nip</li>
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<li>laser pointers</li>
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<li>lasagna</li>
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</ul>
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<p>Top 3 things cats hate:</p>
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<ol>
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<li>flea treatment</li>
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<li>thunder</li>
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<li>other cats</li>
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</ol>
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</div>
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<form action="https://freecatphotoapp.com/submit-cat-photo">
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<label><input type="radio" name="indoor-outdoor" checked> Indoor</label>
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<label><input type="radio" name="indoor-outdoor"> Outdoor</label><br>
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<label><input type="checkbox" name="personality" checked> Loving</label>
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<label><input type="checkbox" name="personality"> Lazy</label>
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<label><input type="checkbox" name="personality"> Energetic</label><br>
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<input type="text" placeholder="cat photo URL" required>
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<button type="submit">Submit</button>
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</form>
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</main>
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```
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# --solutions--
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```html
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<style>
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.red-text {
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color: red;
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}
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</style>
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<h2 class="red-text">CatPhotoApp</h2>
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<main>
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<p>Click here to view more <a href="#">cat photos</a>.</p>
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<a href="#"><img src="https://cdn.freecodecamp.org/curriculum/cat-photo-app/relaxing-cat.jpg" alt="A cute orange cat lying on its back."></a>
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<div>
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<p>Things cats love:</p>
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<ul>
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<li>cat nip</li>
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<li>laser pointers</li>
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<li>lasagna</li>
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</ul>
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<p>Top 3 things cats hate:</p>
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<ol>
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<li>flea treatment</li>
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<li>thunder</li>
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<li>other cats</li>
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</ol>
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</div>
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<form action="https://freecatphotoapp.com/submit-cat-photo">
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<label><input type="radio" name="indoor-outdoor" checked> Indoor</label>
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<label><input type="radio" name="indoor-outdoor"> Outdoor</label><br>
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<label><input type="checkbox" name="personality" checked> Loving</label>
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<label><input type="checkbox" name="personality"> Lazy</label>
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<label><input type="checkbox" name="personality"> Energetic</label><br>
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<input type="text" placeholder="cat photo URL" required>
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<button type="submit">Submit</button>
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</form>
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</main>
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```
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