---
id: 5a9d7295424fe3d0e10cad14
challengeType: 0
videoUrl: 'https://scrimba.com/c/cyLZZhZ'
forumTopicId: 301088
localeTitle: 继承 CSS 变量
---

## Description
<section id='description'>
当创建一个变量时，变量会在创建的选择器里可用。同时，在这个选择器的后代里面也是可用的。这是因为 CSS 变量是可继承的，和普通的属性一样。
CSS 变量经常会定义在  <dfn>:root</dfn> 元素内，这样就可被所有选择器继承。<code>:root</code> 是一个 <dfn>pseudo-class</dfn> 选择器匹配文档的根选择器，通常指 <code>html</code> 元素。通过在 <code>:root</code> 里创建变量，变量在全局可用，以及在 style 样式的选择器里也生效。
</section>

## Instructions
<section id='instructions'>
在 <code>:root</code> 选择器里定义变量 <code>--penguin-belly</code> 并赋值 <code>pink</code>。会发现变量被继承，所有使用该变量的子元素都会有 pink 背景。
</section>

## Tests
<section id='tests'>

```yml
tests:
  - text: '应该在 <code>:root</code> 里声明 <code>--penguin-belly</code> 变量并赋值 <code>pink</code>。'
    testString: assert(code.match(/:root\s*?{[\s\S]*--penguin-belly\s*?:\s*?pink\s*?;[\s\S]*}/gi));

```

</section>

## Challenge Seed
<section id='challengeSeed'>

<div id='html-seed'>

```html
<style>
  :root {

    /* add code below */

    /* add code above */
  }

  body {
    background: var(--penguin-belly, #c6faf1);
  }

  .penguin {
    --penguin-skin: gray;
    --penguin-beak: orange;
    position: relative;
    margin: auto;
    display: block;
    margin-top: 5%;
    width: 300px;
    height: 300px;
  }

  .right-cheek {
    top: 15%;
    left: 35%;
    background: var(--penguin-belly, white);
    width: 60%;
    height: 70%;
    border-radius: 70% 70% 60% 60%;
  }

  .left-cheek {
    top: 15%;
    left: 5%;
    background: var(--penguin-belly, white);
    width: 60%;
    height: 70%;
    border-radius: 70% 70% 60% 60%;
  }

  .belly {
    top: 60%;
    left: 2.5%;
    background: var(--penguin-belly, white);
    width: 95%;
    height: 100%;
    border-radius: 120% 120% 100% 100%;
  }

  .penguin-top {
    top: 10%;
    left: 25%;
    background: var(--penguin-skin, gray);
    width: 50%;
    height: 45%;
    border-radius: 70% 70% 60% 60%;
  }

  .penguin-bottom {
    top: 40%;
    left: 23.5%;
    background: var(--penguin-skin, gray);
    width: 53%;
    height: 45%;
    border-radius: 70% 70% 100% 100%;
  }

  .right-hand {
    top: 0%;
    left: -5%;
    background: var(--penguin-skin, gray);
    width: 30%;
    height: 60%;
    border-radius: 30% 30% 120% 30%;
    transform: rotate(45deg);
    z-index: -1;
  }

  .left-hand {
    top: 0%;
    left: 75%;
    background: var(--penguin-skin, gray);
    width: 30%;
    height: 60%;
    border-radius: 30% 30% 30% 120%;
    transform: rotate(-45deg);
    z-index: -1;
  }

  .right-feet {
    top: 85%;
    left: 60%;
    background: var(--penguin-beak, orange);
    width: 15%;
    height: 30%;
    border-radius: 50% 50% 50% 50%;
    transform: rotate(-80deg);
    z-index: -2222;
  }

  .left-feet {
    top: 85%;
    left: 25%;
    background: var(--penguin-beak, orange);
    width: 15%;
    height: 30%;
    border-radius: 50% 50% 50% 50%;
    transform: rotate(80deg);
    z-index: -2222;
  }

  .right-eye {
    top: 45%;
    left: 60%;
    background: black;
    width: 15%;
    height: 17%;
    border-radius: 50%;
  }

  .left-eye {
    top: 45%;
    left: 25%;
    background: black;
    width: 15%;
    height: 17%;
    border-radius: 50%;
  }

  .sparkle {
    top: 25%;
    left: 15%;
    background: white;
    width: 35%;
    height: 35%;
    border-radius: 50%;
  }

  .blush-right {
    top: 65%;
    left: 15%;
    background: pink;
    width: 15%;
    height: 10%;
    border-radius: 50%;
  }

  .blush-left {
    top: 65%;
    left: 70%;
    background: pink;
    width: 15%;
    height: 10%;
    border-radius: 50%;
  }

  .beak-top {
    top: 60%;
    left: 40%;
    background: var(--penguin-beak, orange);
    width: 20%;
    height: 10%;
    border-radius: 50%;
  }

  .beak-bottom {
    top: 65%;
    left: 42%;
    background: var(--penguin-beak, orange);
    width: 16%;
    height: 10%;
    border-radius: 50%;
  }

  .penguin * {
    position: absolute;
  }
</style>
<div class="penguin">
  <div class="penguin-bottom">
    <div class="right-hand"></div>
    <div class="left-hand"></div>
    <div class="right-feet"></div>
    <div class="left-feet"></div>
  </div>
  <div class="penguin-top">
    <div class="right-cheek"></div>
    <div class="left-cheek"></div>
    <div class="belly"></div>
    <div class="right-eye">
      <div class="sparkle"></div>
    </div>
    <div class="left-eye">
      <div class="sparkle"></div>
    </div>
    <div class="blush-right"></div>
    <div class="blush-left"></div>
    <div class="beak-top"></div>
    <div class="beak-bottom"></div>
  </div>
</div>
```

</div>



</section>

## Solution
<section id='solution'>


```js
var code = ":root {--penguin-belly: pink;}"
```

</section>