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With the basics of positioning covered in the last article, we will now look at building some real world examples, to illustrate what kinds of things you can do with positioning.




HTML basics (study Introduction to HTML), and an idea of How CSS works (study Introduction to CSS.)



To get an idea of the practicalities of positioning

A tabbed info-box


The first example we'll look at is a classic tabbed info box — a very common feature used when you want to pack a lot of information into a small area. This includes information-heavy apps like strategy/war games, mobile versions of websites where the screen is narrow and space is limited, and compact information boxes where you might want to make lots of information available without having it fill the whole UI. Our simple example will look like this once we are finished:



Note: You can see the finished example running live at info-box.html (source code). Check it out to get an idea of what you will be building in this section of the article.


You might be thinking "why not just create the separate tabs as separate webpages, and just have the tabs clicking through to the separate pages to create the effect?" This code would be simpler, yes, but then each separate "page" view would actually be a newly-loaded webpage, which would make it harder to save information across views, and integrate this feature into a larger UI design. In addition, so-called "single page apps" are becoming very popular — especially for mobile web UIs — because having everything served as a single file cuts down on the number of HTTP requests required to view all the content, thereby improving performance.


Note: Some web developers take things even further, only having one page of information loaded at once, and dynamically changing the information shown using a JavaScript feature such as XMLHttpRequest. At this point in your learning however we want to keep things as simple as possible. There is some JavaScript later on, but only a tiny bit.


To start with, we'd like you to make a local copy of the starting HTML file — info-box-start.html. Save this somewhere sensible on your local computer, and open it up in your text editor. Let's look at the HTML contained within the body:


<section class="info-box">
    <li><a href="#" class="active">Tab 1</a></li>
    <li><a href="#">Tab 2</a></li>
    <li><a href="#">Tab 3</a></li>
  <div class="panels">
    <article class="active-panel">
      <h2>The first tab</h2>

      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Pellentesque turpis nibh, porttitor nec venenatis eu, pulvinar in augue. Vestibulum et orci scelerisque, vulputate tellus quis, lobortis dui. Vivamus varius libero at ipsum mattis efficitur ut nec nisl. Nullam eget tincidunt metus. Donec ultrices, urna maximus consequat aliquet, dui neque eleifend lorem, a auctor libero turpis at sem. Aliquam ut porttitor urna. Nulla facilisi.</p>
      <h2>The second tab</h2>

      <p>This tab hasn't got any Lorem Ipsum in it. But the content isn't very exciting all the same.</p>
      <h2>The third tab</h2>

      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Pellentesque turpis nibh, porttitor nec venenatis eu, pulvinar in augue. And now an ordered list: how exciting!</p>

        <li>dui neque eleifend lorem, a auctor libero turpis at sem.</li>
        <li>Aliquam ut porttitor urna.</li>
        <li>Nulla facilisi</li>

So here we've got a <section> element with a class of info-box, which contains a <ul> and a <div>. The unordered list contains three list items with links inside, which will become the actual tabs to click on for displaying our content panels. The div contains three <article> elements, which will make up the content panels that correspond to each tab. Each panel contains some sample content.

现在我们在info-box类里已经得到了一个section元素。元素包含一个ul和一个div。这个无序列表包含三个内部链接列表项(li),这实际将成为点击后显示内容面板的选项卡。Div标签包含三个article元素,这将构成对应于每个选项卡的内容面板。 每个面板包含一些示例内容。

The idea here is that we will style the tabs to look like a standard horizontal navigation menu, and style the panels to sit on top of one another using absolute positioning. We'll also give you a bit of JavaScript to include on your page to display the corresponding panel when a tab is pressed, and style the tab itself. You won't need to understand the JavaScript itself at this stage, but you should think about learning some basic JavaScript as soon as possible — the more complex your UI features become, the more likely it is that you'll need some JavaScript to implement your desired functionality.


General setup


To begin with, add the following between your opening and closing <style> tags:


html {
  font-family: sans-serif;

* {
  box-sizing: border-box;

body {
  margin: 0;

This is just some general setup to set a sans-serif font on our page, use the border-box box-sizing model, and get rid of the default <body> margin.

Next, add the following just below your previous CSS:



.info-box {
  width: 450px;
  height: 400px;
  margin: 0 auto;

This sets a specific width and height on the content, and centers it on the screen using the old margin: 0 auto trick. Previously in the course we advised against setting a fixed height on content containers if at all possible; it is ok in this circumstance because we have fixed content in our tabs. It also looks a bit jarring to have different tabs at different heights.

对内容设置特别的高度和宽度,在使用古老的margin:0 auto 把戏,实现在屏幕居中。在早先的课程中我们建议反对设置内容容器固定的宽度,如果可能的话。在这里是允许的,因为我们固定我们标签的内容,如果每个标签都有不同的高度,看起来也有些不和谐。

Styling our tabs


Now we want to style tabs to look like tabs — basically, these are a horizontal navigation menu, but instead of loading different web pages when they are clicked on like we've seen previously in the course, they cause different panels to be displayed on the same page. First, add the following rule at the bottom of your CSS to remove the default padding-left and margin-top from the unordered list:

现在我们要让标签样式看起来更像标签——基本的,这里有一个水平的导航标签,但是和我们之前学的点击之后加载不同的界面,他们会显示不同的面板在同一个界面上。首先,在你的CSS底部添加下列规则,来从无序列表中移除默认的padding-left和margin-top 值:

.info-box ul {
  padding-left: 0;
  margin-top: 0;

Note: We are using descendant selectors with .info-box at the start of the chain throughout this example — this is so that we can insert this feature into a page with other content already on it, without fear of interfering with the styles applied to other parts of the page.

笔记:这个例子开始的链,我们使用.info-box 选择器的后裔——这样我们就能插入一个已经有其他内容的页面,不用担心干扰页面的其他部分。

Next, we'll style the horizontal tabs — the list items are all floated left to make them sit in a line together, their list-style-type is set to none to get rid of the bullets, and their width is set to 150px so they will comfortably fit across the info-box. The <a> elements are set to display inline-block so they will sit in a line but still be stylable, and they are styled appropriately for tab buttons, using a variety of other properties.

Add the following CSS:



.info-box li {
  float: left;
  list-style-type: none;
  width: 150px;

.info-box li a {
  display: inline-block;
  text-decoration: none;
  width: 100%;
  line-height: 3;
  background-color: red;
  color: black;
  text-align: center;

Finally for this section we'll set some styles on the link states. First, we'll set the :focus and :hover states of the tabs to look different when they are focused/hovered, providing users with some visual feedback. Secondly, we'll set a rule that puts the same styling on one of the tabs when a class of active is present on it. We will set this using JavaScript when a tab is clicked on. Place the following CSS below your other styles:

最后,对于这些section,我们将会设置一些样式在链接声明上。首先,我们要设置标签的focus 和 hover属性,让他们在聚焦/鼠标悬浮的时候看起来不同,给用户提供一些可视化反馈。其次,我们设置一条规则,使用相同的样式当active已经在其中已经使用过的标签,我们将通过使用来设置,当一个标签被点击。把这些CSS放置在你的其他样式后面:

.info-box li a:focus, .info-box li a:hover {
  background-color: #a60000;
  color: white;

.info-box li {
  background-color: #a60000;
  color: white;

Styling the panels


The next job is to style our panels. Let's get going!

First, of all, add the following rule to style the .panels <div> container. Here we simply set a fixed height to make sure the panels fit snugly inside the info-box, position relative to set the <div> as the positioning context, so you can then place positioned child elements relative to it and not the <html> element, and finally we clear the float set in the CSS above so that it doesn't interfere with the remainder of the layout.


首先,添加下列的规则到样式 .panels容器中。我们简单的设置固定的高度属性确保panels紧紧的包含在info-box里面,将其设置为相对定位,以div为参考。所以你能把子元素以相对定位放置,不是以html元素为参考,最后我们清除浮动,避免影响其他的层。

.info-box .panels {
  height: 352px;
  position: relative;
  clear: both;

Finally for this section, we will style the individual <article> elements that comprise our panels. The first rule we'll add will absolutely position the panels, and make them all sit flush to the top and left of their <div> container — this part is absolutely key to this whole layout feature, as it makes the panels sit on top of one another. The rule also gives the panels the same set height as the container, and gives the content some padding, a text color, and a background-color.

在这个section的最后,我们将对包含在我们面板内的article元素设置单独的样式。我们添加的第一条规则就是相对于面板的绝对定位,让他们对齐div容器的顶部和左边——这一部分对整个层的特性是关键的,就像使面板位于其他内容的顶部。规则同样给面板和容器同样的高度,给内容一些padding 边距,设置字体颜色,和背景颜色。

The second rule we'll add here makes it so that a panel with a class of active-panel set on it will have a z-index of 1 applied to it, which will make it sit above the other panels (positioned elements have a z-index of 0 by default, which would put them below). Again, we'll add this class using JavaScript at the appropriate time.



.info-box article {
  position: absolute;
  top: 0;
  left: 0;
  height: 352px;
  padding: 10px;
  color: white;
  background-color: #a60000;

.info-box .active-panel {
  z-index: 1;

Adding our JavaScript


The final step to getting this feature working is to add some JavaScript. Put the following block of code, exactly as written in between your opening and closing <script> tags (you'll find these below the HTML content):


var tabs = document.querySelectorAll('.info-box li a');
var panels = document.querySelectorAll('.info-box article');

for(i = 0; i < tabs.length; i++) {
  var tab = tabs[i];
  setTabHandler(tab, i);

function setTabHandler(tab, tabPos) {
  tab.onclick = function() {
    for(i = 0; i < tabs.length; i++) {
      if(tabs[i].getAttribute('class')) {

    tab.setAttribute('class', 'active');

    for(i = 0; i < panels.length; i++) {
      if(panels[i].getAttribute('class')) {

    panels[tabPos].setAttribute('class', 'active-panel');

This code does the following:

  • First we save a reference to all the tabs and all the panels in two variables called tabs and panels, so we can easily do things to them later on.
  • Then we use a for loop to cycle through all the tabs and run a function called setTabHandler() on each one, which sets up the functionality that should occur when each one is clicked on. When run, the function is passed a reference to the particular tab it is being run for, and an index number i that indentifies the tab's position in the tabs array.
  • In the setTabHandler() function, the tab has an onclick event handler set on it, so that when the tab is clicked, the following occurs:
    • A for loop is used to cycle through all the tabs and remove any classes that are present on them.
    • A class of active is set on the tab that was clicked on — remember from earlier that this class has an associated rule in the CSS that sets the same color and background-color on the tab as the panels are styled with.
    • A for loop is used to cycle through all the panels and remove any classes that are present on them.
    • A class of active-panel is set on the panel that corresponds to the tab that was clicked on — remember from earlier that this class has an associated rule in the CSS that sets its z-index to 1, making it appear over the top of the other panels.

That's it for the first example. Keep your code open, as we'll be adding to it in the second one.



接下来我们用一个for循环对所有的tab属性运行setTabHandler()函数,当各自被点击发生时实现功能 。当运行时,这个函数被作为引用传递给特定的现有的运行的标签。目录数字 i 被用来标明标签在tabs数组中的位置。



当点击的时候在标签上创建了一个active 类——从相关联的元素中继承了CSS的一些属性,具有和panels的样式相同的颜色,背景颜色。


当标签被点击的时候在和标签相对应的面板上创建了一个active-panel 类——从相关联的元素中继承了CSS的一些属性,使他的z-index属性被设置为1,让他能位于所有的面板的上面。


A fixed position tabbed info-box


In our second example, we will take our first example — our info-box — and add it into the context of a full web page. But not only that — we'll give it fixed position so that it stays in the same position in the browser window. When the main content scrolls, the info-box will stay in the same position on the screen. Our finished example will look like this:


Note: You can see the finished example running live at fixed-info-box.html (source code). Check it out to get an idea of what you will be building in this section of the article.


As a starting point, you can use your completed example from the first section of the article, or make a local copy of info-box.html from our Github repo.


HTML additions


First of all, we need some additional HTML to represent the web site main content. Add the following <section> just below your opening <body> tag, just before the existing section:


<section class="fake-content">
  <h1>Fake content</h1>
  <p>This is fake content. Your main web page contents would probably go here.</p>
  <p>This is fake content. Your main web page contents would probably go here.</p>
  <p>This is fake content. Your main web page contents would probably go here.</p>
  <p>This is fake content. Your main web page contents would probably go here.</p>
  <p>This is fake content. Your main web page contents would probably go here.</p>
  <p>This is fake content. Your main web page contents would probably go here.</p>
  <p>This is fake content. Your main web page contents would probably go here.</p>
  <p>This is fake content. Your main web page contents would probably go here.</p>

Note: You can feel free to change the fake content for some real content if you like.


Changes to the existing CSS


Next we need to make some small changes to the existing CSS, to get the info-box placed and positioned. Change your .info-box rule to get rid of margin: 0 auto; (we no longer want the info-box centered), add position: fixed;, and stick it to the top of the browser viewport.

It should now look like this:

接下来我们需要对之前的Css进行一些小修改,让消息盒子放置和定位的好一些。删除你的margin: 0 auto (不需要居中显示),添加fixed定位;调整top 属性把她粘在浏览器的视域。

.info-box {
  width: 450px;
  height: 400px;
  position: fixed;
  top: 0;

Styling the main content


The only thing left for this example is to provide the main content with some styling. Add the following rule underneath the rest of your CSS:

对于这个例子来说唯一剩下的事情就是给主内容提供一些样式设计。添加下面的规则到你剩下的Css 的下面:

.fake-content {
  background-color: #a60000;
  color: white;
  padding: 10px;
  height: 2000px;
  margin-left: 470px;

To start with, we give the content the same background-color, color, and padding as the info-box panels. We then give it a large margin-left to move it over to the right, making space for the info-box to sit in, so it is not overlapping anything else.

This marks the end of the second example; we hope you'll find the third just as interesting.



A sliding hidden panel


The final example we'll present here is a panel that slides on and off the screen at the press of an icon — as mentioned earlier, this is popular for situations like mobile layouts, where the available screen spaces is small, so you don't want to use up most of it by showing a menu or info panel instead of the useful content.


Our finished example will look like this:


Note: You can see the finished example running live at hidden-info-panel.html (source code). Check it out to get an idea of what you will be building in this section of the article.


As a starting point, make a local copy of hidden-info-panel-start.html from our Github repo. This doesn't follow on from the previous example, so a fresh start file is required. Let's have a look at the HTML in the file:


<label for="toggle">❔</label>
<input type="checkbox" id="toggle">



To start with here we've got a <label> element and an <input> element — <label> elements are normally used to associate a text label with a form element for accessibility purposes (allowing a screen user to see what description goes with what form element). Here it is associated with the <input> checkbox using the for and id attributes.

//label 的 for属性规定label属性绑定到哪个表单元素。

开始,我们看到了一个label 元素和input元素——<label>元素普遍用来联系文字标签和表单,目的是能更好的理解表单(允许用户查看表单元素的描述)。这里通过for属性绑定id到了<input>标签的checkbox元素。


Note: We've put a special question mark character into our HTML to act as our info icon — this represents the button that will be pressed to show/hide the panel.


Here we are going to use these elements for a slightly different purpose — another useful side effect of <label> elements is that you can click a checkbox's label to check the checkbox, as well as just the checkbox itself. This has led to the well-known checkbox hack, which provides a JavaScript-free way of controlling an element by toggling a button. The element we'll be controlling is the <aside> element that follows the other two (we've left its contents out of the above code listing for brevity).

In the below sections we'll explain how this all works.

现在我们使用这些元素在稍稍不同的目的——另一个<label>标签有用的副作用使你能通过点击checkbox的label标签来选择这个checkbox,就好像点击了这个checkbox自己一样。这就会实现有名的checkbox hack 技术,可以提供无JS的方法来控制一个元素,通过一个按钮的联系。我们将控制的元素使aside元素,通过其他两个(为了简洁起见,我们已将其内容从上述代码列表中删除)。


Styling the form elements


First let's deal with the form elements — add the following CSS in between your <style> tags:

首先让我们处理表单元素 - 在style标签之间添加以下CSS:

label[for="toggle"] {
  font-size: 3rem;
  position: absolute;
  top: 4px;
  right: 5px;
  z-index: 1;
  cursor: pointer;

input[type="checkbox"] {
  position: absolute;
  top: -100px;

The first rule styles the <label>; here we've:

  • Set a large font-size to make the icon nice and big.
  • Set position absolute on it, and used top and right to position it nicely in the top-right corner.
  • Set a z-index of 1 on it — this is so that when the info panel is styled and shown, it doesn't cover up the icon; instead the icon will sit on top of it so it can be pressed again to hide the info pane.
  • Used the cursor property to change the mouse cursor when it is hovering over the icon to a hand pointer (like the one you see when links are hovered over), as an extra visual clue to users that the icon does something interesting.

The second rule sets position absolute on the actual checkbox <input> element, and hides it off the top of the screen. We don't actually want to see this on our UI.







Styling the panel


Now it's time to style the actual sliding panel itself. Add the following rule to the bottom of your CSS:


aside {
  background-color: #a60000;
  color: white;

  width: 340px;
  height: 98%;
  padding: 10px 1%;

  position: fixed;
  top: 0;
  right: -370px;

  transition: 0.6s all;

There's a lot going on here — let's discuss it bit by bit:

  • First, we set some simple background-color and color on the info box.
  • Next, we set a fixed width on the panel, and make its height the entire height of the browser viewport.
  • We also include some padding to make up the width/height to the total value we want (this was necessary as we've not set box-sizing: border-box; on this example).
  • Next we set position: fixed; on the panel so it will always appear in the same place, even if the page has content to scroll. We glue it to the top of the viewport, and set it so that by default it is offscreen to the right.
  • Finally, we set a transition on the element. Transitions are an interesting feature that allow you to make changes between states happen smoothly, rather than just going "on", "off" abruptly. In this case we are intending to make the panel slide smoothly onscreen when the checkbox is checked. (Or to put it another way, when the question mark icon is clicked — remember, clicking the <label> will check the associated checkbox! We told you it was a hack.) You will learn a lot more about...








Setting the checked state


There is one final bit of CSS to add — put the following at the bottom of your CSS:


input[type=checkbox]:checked + aside {
  right: 0px;

The selector is pretty complex here — we are selecting the <aside> element adjacent to the <input> element, but only when it is checked (note the use of the :checked pseudo-class to achieve this). When this is the case, we are setting the right property of the <aside> to 0px, which causes the panel to appear on the screen again (smoothly due to the transition). Clicking the label again unchecks the checkbox, which hides the panel again.


So there you have it — a rather clever JavaScript-free way to create a toggling button effect. This will work in IE9 and above (the smooth transition will work in IE10 and above.) This effect does have some concerns — this is a bit of an abuse of form elements (they weren't intended for this purpose), and the effect is not great in terms of accessibilty — the label is not focusable by default, and the non-semantic use of the form elements could cause issues with screenreaders. JavaScript and a link or button might be more appropriate, but it is still fun to experiment with.

所以你有它 ——一个相当巧妙的避免使用JavaScript来创建一个切换按钮效果方式。 这将在IE9及以上版本中起作用(平滑过渡将在IE10及更高版本中起作用)。这种效果确实有一些问题 ——这是有点滥用表单元素(它们不是为了这个目的),并且在可访问性方面效果不是很好 - 标签在默认情况下不可聚焦,并且表单元素的非语义使用可能会导致屏幕朗读器出现问题。 JavaScript和链接或按钮可能更合适,但这样的实验仍然很有趣。



So that rounds off our look at positioning — by now, you should have an idea of how the basic mechanics work,as well as understanding how to start applying these to building some interesting UI features. Don't worry if you didn't get this all immediately — positioning is a fairly advanced topic, and you can always work through the articles again to aid your understanding. The next subject we'll turn to is Flexbox.



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