2018-10-10 22:03:03 +00:00
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---
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id: 587d781e367417b2b2512acc
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2020-12-16 07:37:30 +00:00
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title: 固定定位的参照物是浏览器的窗口
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2018-10-10 22:03:03 +00:00
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challengeType: 0
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2020-02-11 07:46:34 +00:00
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videoUrl: 'https://scrimba.com/c/c2MDNUR'
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forumTopicId: 301061
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2021-01-13 02:31:00 +00:00
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dashedName: lock-an-element-to-the-browser-window-with-fixed-positioning
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2018-10-10 22:03:03 +00:00
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---
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2020-12-16 07:37:30 +00:00
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# --description--
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2018-10-10 22:03:03 +00:00
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2021-01-08 19:20:48 +00:00
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接下来要介绍的是 `fixed` 定位，它是一种特殊的绝对（absolute）定位，区别是其包含块是浏览器窗口。和绝对定位类似，在 `fixed` 定位的元素中，我们也可以使用 top、bottom、left、right 属性来调整元素的位置，并且也会将元素从当前的文档流里面移除，其它元素会忽略它的存在。
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2018-10-10 22:03:03 +00:00
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2021-01-08 19:20:48 +00:00
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但 `fixed` 和 `absolute` 的最明显的区别在于，`fixed` 定位元素不会随着屏幕滚动而移动。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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# --instructions--
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2018-10-10 22:03:03 +00:00
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2021-01-08 19:20:48 +00:00
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我们已经将代码里导航栏的 id 设置为了 `navbar`。请把它的 `position` 设置成 `fixed`，同时分别设定其 `top` 和 `left` 属性值为 0 像素。修改后，你可以滑动预览窗口，观察导航栏的位置。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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# --hints--
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2018-10-10 22:03:03 +00:00
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2021-01-08 19:20:48 +00:00
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`#navbar` 元素的 `position` 属性值应为 `fixed`。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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```js
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assert($('#navbar').css('position') == 'fixed');
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2018-10-10 22:03:03 +00:00
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```
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2021-01-08 19:20:48 +00:00
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`#navbar` 元素的 `top` 属性值应为 `0px`。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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```js
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assert($('#navbar').css('top') == '0px');
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```
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2018-10-10 22:03:03 +00:00
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2021-01-08 19:20:48 +00:00
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`#navbar` 元素的 `left` 属性值应为 `0px`。
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2018-10-10 22:03:03 +00:00
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2020-12-16 07:37:30 +00:00
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```js
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assert($('#navbar').css('left') == '0px');
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2018-10-10 22:03:03 +00:00
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```
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2020-02-11 07:46:34 +00:00
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2021-01-13 02:31:00 +00:00
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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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body {
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min-height: 150vh;
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}
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#navbar {
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width: 100%;
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background-color: #767676;
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}
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nav ul {
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margin: 0px;
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padding: 5px 0px 5px 30px;
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}
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nav li {
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display: inline;
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margin-right: 20px;
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}
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a {
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text-decoration: none;
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}
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</style>
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<body>
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<header>
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<h1>Welcome!</h1>
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<nav id="navbar">
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<ul>
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<li><a href="">Home</a></li>
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<li><a href="">Contact</a></li>
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</ul>
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</nav>
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</header>
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<p>I shift up when the #navbar is fixed to the browser window.</p>
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</body>
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```
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2020-12-16 07:37:30 +00:00
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# --solutions--
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2021-01-13 02:31:00 +00:00
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```html
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<style>
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body {
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min-height: 150vh;
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}
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#navbar {
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position: fixed;
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top: 0;
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left: 0;
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width: 100%;
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background-color: #767676;
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}
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nav ul {
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margin: 0px;
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padding: 5px 0px 5px 30px;
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}
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nav li {
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display: inline;
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margin-right: 20px;
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}
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a {
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text-decoration: none;
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}
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</style>
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<body>
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<header>
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<h1>Welcome!</h1>
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<nav id="navbar">
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<ul>
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<li><a href="">Home</a></li>
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<li><a href="">Contact</a></li>
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</ul>
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</nav>
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</header>
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<p>I shift up when the #navbar is fixed to the browser window.</p>
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</body>
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```
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