2018-10-10 18:03:03 -04:00
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---
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id: 5a9d7295424fe3d0e10cad14
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2020-12-16 00:37:30 -07:00
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title: 继承 CSS 变量
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2018-10-10 18:03:03 -04:00
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challengeType: 0
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2019-12-13 13:47:57 +08:00
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videoUrl: 'https://scrimba.com/c/cyLZZhZ'
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forumTopicId: 301088
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2021-01-13 03:31:00 +01:00
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dashedName: inherit-css-variables
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2018-10-10 18:03:03 -04:00
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---
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2020-12-16 00:37:30 -07:00
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# --description--
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2018-10-10 18:03:03 -04:00
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2021-01-08 11:20:48 -08:00
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当创建一个变量时,变量会在创建变量的选择器里可用。同时,在这个选择器的后代选择器里也是可用的。这是因为 CSS 变量是可继承的,和普通的属性一样。
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2018-10-10 18:03:03 -04:00
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2021-01-08 11:20:48 -08:00
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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。
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`:root` 是一个<dfn>伪类</dfn>选择器,它是一个能够匹配文档根元素的选择器,通常指的是 `html` 元素。我们在 `:root` 里创建变量在全局都可用,即在任何选择器里都生效。
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2018-10-10 18:03:03 -04:00
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2020-12-16 00:37:30 -07:00
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# --instructions--
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2018-10-10 18:03:03 -04:00
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2021-01-08 11:20:48 -08:00
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在 `:root` 选择器里定义变量 `--penguin-belly` 并设置它的属性值为 `pink`。此时,你会发现变量被继承,所有使用该变量的子元素都会有粉色背景。
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2018-10-10 18:03:03 -04:00
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2020-12-16 00:37:30 -07:00
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# --hints--
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2018-10-10 18:03:03 -04:00
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2021-01-08 11:20:48 -08:00
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应在 `:root` 里声明 `--penguin-belly` 变量并赋值 `pink`。
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2019-12-13 13:47:57 +08:00
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2018-10-10 18:03:03 -04:00
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```js
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2020-12-16 00:37:30 -07:00
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assert(
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code.match(/:root\s*?{[\s\S]*--penguin-belly\s*?:\s*?pink\s*?;[\s\S]*}/gi)
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);
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2018-10-10 18:03:03 -04:00
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```
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2019-12-13 13:47:57 +08:00
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2021-01-13 03:31:00 +01:00
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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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:root {
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/* Only change code below this line */
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/* Only change code above this line */
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}
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body {
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background: var(--penguin-belly, #c6faf1);
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}
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.penguin {
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--penguin-skin: gray;
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--penguin-beak: orange;
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position: relative;
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margin: auto;
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display: block;
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margin-top: 5%;
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width: 300px;
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height: 300px;
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}
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.right-cheek {
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top: 15%;
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left: 35%;
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background: var(--penguin-belly, white);
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width: 60%;
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height: 70%;
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border-radius: 70% 70% 60% 60%;
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}
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.left-cheek {
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top: 15%;
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left: 5%;
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background: var(--penguin-belly, white);
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width: 60%;
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height: 70%;
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border-radius: 70% 70% 60% 60%;
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}
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.belly {
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top: 60%;
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left: 2.5%;
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background: var(--penguin-belly, white);
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width: 95%;
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height: 100%;
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border-radius: 120% 120% 100% 100%;
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}
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.penguin-top {
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top: 10%;
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left: 25%;
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background: var(--penguin-skin, gray);
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width: 50%;
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height: 45%;
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border-radius: 70% 70% 60% 60%;
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}
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.penguin-bottom {
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top: 40%;
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left: 23.5%;
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background: var(--penguin-skin, gray);
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width: 53%;
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height: 45%;
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border-radius: 70% 70% 100% 100%;
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}
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.right-hand {
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top: 0%;
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left: -5%;
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background: var(--penguin-skin, gray);
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width: 30%;
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height: 60%;
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border-radius: 30% 30% 120% 30%;
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transform: rotate(45deg);
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z-index: -1;
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}
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.left-hand {
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top: 0%;
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left: 75%;
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background: var(--penguin-skin, gray);
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width: 30%;
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height: 60%;
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border-radius: 30% 30% 30% 120%;
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transform: rotate(-45deg);
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z-index: -1;
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}
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.right-feet {
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top: 85%;
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left: 60%;
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background: var(--penguin-beak, orange);
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width: 15%;
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height: 30%;
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border-radius: 50% 50% 50% 50%;
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transform: rotate(-80deg);
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z-index: -2222;
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}
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.left-feet {
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top: 85%;
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left: 25%;
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background: var(--penguin-beak, orange);
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width: 15%;
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height: 30%;
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border-radius: 50% 50% 50% 50%;
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transform: rotate(80deg);
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z-index: -2222;
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}
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.right-eye {
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top: 45%;
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left: 60%;
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background: black;
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width: 15%;
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height: 17%;
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border-radius: 50%;
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}
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.left-eye {
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top: 45%;
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left: 25%;
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background: black;
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width: 15%;
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height: 17%;
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border-radius: 50%;
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}
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.sparkle {
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top: 25%;
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left: 15%;
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background: white;
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width: 35%;
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height: 35%;
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border-radius: 50%;
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}
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.blush-right {
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top: 65%;
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left: 15%;
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background: pink;
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width: 15%;
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height: 10%;
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border-radius: 50%;
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}
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.blush-left {
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top: 65%;
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left: 70%;
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background: pink;
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width: 15%;
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height: 10%;
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border-radius: 50%;
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}
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.beak-top {
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top: 60%;
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left: 40%;
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background: var(--penguin-beak, orange);
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width: 20%;
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height: 10%;
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border-radius: 50%;
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}
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.beak-bottom {
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top: 65%;
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left: 42%;
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background: var(--penguin-beak, orange);
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width: 16%;
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height: 10%;
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border-radius: 50%;
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}
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.penguin * {
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position: absolute;
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}
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</style>
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<div class="penguin">
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<div class="penguin-bottom">
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<div class="right-hand"></div>
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<div class="left-hand"></div>
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<div class="right-feet"></div>
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<div class="left-feet"></div>
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</div>
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<div class="penguin-top">
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<div class="right-cheek"></div>
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<div class="left-cheek"></div>
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<div class="belly"></div>
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<div class="right-eye">
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<div class="sparkle"></div>
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</div>
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<div class="left-eye">
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<div class="sparkle"></div>
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</div>
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<div class="blush-right"></div>
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<div class="blush-left"></div>
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<div class="beak-top"></div>
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<div class="beak-bottom"></div>
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</div>
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</div>
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```
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2020-12-16 00:37:30 -07:00
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# --solutions--
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2021-01-13 03:31:00 +01:00
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```html
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<style>:root {--penguin-belly: pink;}</style>
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```
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