173 lines
4.5 KiB
Markdown
173 lines
4.5 KiB
Markdown
---
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id: bad87fee1348bd9aedf08808
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title: 字体如何优雅降级
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challengeType: 0
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videoUrl: 'https://scrimba.com/c/cpVKBfQ'
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forumTopicId: 18304
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dashedName: specify-how-fonts-should-degrade
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---
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# --description--
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所有浏览器都有几种默认字体,包括`monospace`、`serif` 和 `sans-serif`。
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在字体不可用的时候,你可以告诉浏览器通过“降级”去使用其他字体。
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如果你想将一个元素的字体设置成 `Helvetica`,但当 `Helvetica` 不可用时,降级使用 `sans-serif` 字体,那么可以这样写:
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```css
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p {
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font-family: Helvetica, sans-serif;
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}
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```
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通用字体名不区分大小写。同时,也不需要使用引号,因为它们是 CSS 中的关键字。
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# --instructions--
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首先,添加 `monospace` 字体到 `h2` 元素里,它现在拥有 `Lobster` 和 `monospace` 两种字体。
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在上一个挑战里,你已经通过 `link` 标签从谷歌字体库引入了 `Lobster` 字体。现在让我们使用之前学习的 HTML 注释,将 `Lobster` 字体的引入注释掉,这样一来,引入的 `Lobster` 字体会失效。此时,你会发现 `h2` 元素降级到了 `monospace` 字体。
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**注意:**如果你的电脑里已经安装了 `Lobster` 字体,你就看不到这个降级过程,因为浏览器还是会在你的电脑中找到该字体。
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# --hints--
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`h2` 元素的字体应设置为 `Lobster`。
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```js
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assert(
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$('h2')
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.css('font-family')
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.match(/^"?lobster/i)
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);
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```
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当 `Lobster` 字体失效时,`h2` 元素应该降级使用 `monospace` 字体。
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```js
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assert(
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/\s*h2\s*\{\s*font-family\:\s*(\'|")?Lobster(\'|")?,\s*monospace\s*;\s*\}/gi.test(
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code
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)
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);
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```
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通过添加`<!--`,注释掉 `Lobster` 字体的引入。
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```js
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assert(new RegExp('<!--[^fc]', 'gi').test(code));
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```
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确保注释要以 `-->` 结束。
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```js
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assert(new RegExp('[^fc]-->', 'gi').test(code));
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```
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# --seed--
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## --seed-contents--
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```html
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<link href="https://fonts.googleapis.com/css?family=Lobster" rel="stylesheet" type="text/css">
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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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h2 {
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font-family: Lobster;
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}
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p {
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font-size: 16px;
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font-family: monospace;
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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 class="red-text">Click here to view more <a href="#">cat photos</a>.</p>
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<a href="#"><img src="https://bit.ly/fcc-relaxing-cat" 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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<!--<link href="https://fonts.googleapis.com/css?family=Lobster" rel="stylesheet" type="text/css">-->
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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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h2 {
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font-family: Lobster, monospace;
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}
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p {
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font-size: 16px;
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font-family: monospace;
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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 class="red-text">Click here to view more <a href="#">cat photos</a>.</p>
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<a href="#"><img src="https://bit.ly/fcc-relaxing-cat" 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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