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index.html
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index.html
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<!DOCTYPE html>
<!--
Google HTML5 slide template
Authors: Luke Mah (code)
Marcin Wichary (code and design)
Dominic Mazzoni (browser compatibility)
Charles Chen (ChromeVox support)
URL: http://code.google.com/p/html5slides/
-->
<!--
Become a CSS Pro
Author: Jeff Horak
July 2012
URL: http://jmhorak.github.com/css-overview
-->
<html xmlns="http://www.w3.org/1999/html">
<head>
<title>Become a CSS Pro</title>
<meta charset='utf-8'>
<script
src='http://html5slides.googlecode.com/svn/trunk/slides.js'></script>
<link href='http://fonts.googleapis.com/css?family=IM+Fell+English+SC' rel='stylesheet' type='text/css'>
<script type="text/javascript">
var _gaq = _gaq || [];
_gaq.push(['_setAccount', 'UA-33662740-1']);
_gaq.push(['_trackPageview']);
(function() {
var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true;
ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s);
})();
</script>
</head>
<style>
/* Your individual styles here, or just use inline styles if that's
what you want. */
ul.tree li {
margin-bottom: 0;
}
.noWrapping {
white-space: nowrap;
}
div.button {
padding: 3px 11px;
margin: 3px 5px;
background-image: -webkit-linear-gradient(top, whitesmoke, lightgray);
background-image: -moz-linear-gradient(top, whitesmoke, lightgray);
background-image: -ms-linear-gradient(top, whitesmoke, lightgray);
background-image: -o-linear-gradient(top, whitesmoke, lightgray);
background-image: linear-gradient(top, whitesmoke, lightgray);
border: 1px solid gray;
border-radius: 4px;
cursor: default;
box-shadow: 0 1px 1px #202020;
margin: 40px auto;
width: 125px;
text-align: center;
}
div.button:active {
background-image: -webkit-linear-gradient(top, lightgray, whitesmoke);
background-image: -moz-linear-gradient(top, lightgray, whitesmoke);
background-image: -ms-linear-gradient(top, lightgray, whitesmoke);
background-image: -o-linear-gradient(top, lightgray, whitesmoke);
background-image: linear-gradient(top, lightgray, whitesmoke);
box-shadow: inset 1px 1px 4px #202020;
}
div.button:hover {
color: orangered;
}
article.smaller div:not(.source) {
font-size: 20px;
line-height: 24px;
letter-spacing: 0;
}
.fell-English {
font-family: 'IM Fell English SC', serif;
text-rendering: optimizeLegibility;
letter-spacing: 2px;
}
.exampleSpacing {
margin-top: 20px;
}
.text-demo-box {
height: 80px;
width: 120px;
background-color: yellow;
border: 3px solid orange;
font-size: 20px;
}
.segue {
background-image: -webkit-linear-gradient(bottom, lightgray, white 50%);
background-image: -moz-linear-gradient(bottom, lightgray, white 50%);
background-image: -ms-linear-gradient(bottom, lightgray, white 50%);
background-image: -o-linear-gradient(bottom, lightgray, white 50%);
background-image: linear-gradient(bottom, lightgray, white 50%);
}
.colorSegue {
background-image: -webkit-linear-gradient(top, greenyellow, green);
background-image: -moz-linear-gradient(top, greenyellow, green);
background-image: -ms-linear-gradient(top, greenyellow, green);
background-image: -o-linear-gradient(top, greenyellow, green);
background-image: linear-gradient(top, greenyellow, green);
}
.colorTitle {
background-color: rgba(255, 255, 255, 0.2);
text-shadow: 3px 1px 4px #202020;
width: 100%;
right: 0;
text-indent: 40px;
padding-right: 0;
}
.collapseMargin {
margin-top: 20px;
margin-bottom: 10px;
outline: 1px solid red;
}
.box {
border: 3px solid gray;
}
.box1 {
background-color: yellow;
border-color: orangered;
}
.box2 {
background-color: lightblue;
}
.box3 {
background-color: #90ee90;
border-color: green;
}
.box-container {
outline: 1px dashed gray;
}
.bfcDiv {
background-color: orangered;
}
.bfcP {
margin: 20px 0;
background-color: yellow;
}
.bfc-floated-p {
padding: 20px; float: left;
}
.bfc-floated-parent-div {
background-color: lightblue;
}
#performanceResults {
width: 778px;
height: 300px;
}
#performanceDataTable {
font-size: 16px;
line-height: 1.1em;
}
</style>
<body style='display: none'>
<section class='slides layout-regular'>
<!-- Title -->
<article class="segue">
<h1>
Become a CSS Pro
</h1>
<p>Jeff Horak<br>July 5, 2012</p>
<p>Slides:
<a href="http://jmhorak.github.com/css-overview">
http://jmhorak.github.com/css-overview
</a>
</p>
</article>
<!-- Agenda -->
<article>
<h3>
Agenda
</h3>
<ul>
<li>Getting Started</li>
<li>Browser Basics and Tooling</li>
<li>Selectors</li>
<li>Units of Measurement</li>
<li>Layouts</li>
<li>Colors, Shadows, and Gradients</li>
<li>Working with Text</li>
<li>The Story on Vendor Prefixes</li>
<li>SASS</li>
<li>CSS Performance</li>
</ul>
</article>
<!-- Segue to Getting Started -->
<article class="segue">
<h2>Getting Started</h2>
</article>
<!-- Slide Format -->
<article>
<h3>Slide Format</h3>
<p>
All slides were created using <a href="http://code.google.com/p/html5slides/">html5slides</a>.
</p>
<p>
CSS examples are running live - there are no images.
</p>
<div class="source">
A source, citation, or link to further reading provided in this space.
</div>
</article>
<!-- Search like a Pro -->
<article>
<h3>Searching like a Pro</h3>
<p>
Not everyone know everything. Sometimes you need to look at an API.
</p>
<p>
Most of the time, the first hit when searching for any JavaScript/HTML/CSS subject is w3schools.
</p>
<p>
<a href="http://w3fools.com/">W3Schools is bad news</a>. They are a for-profit not in
any way affiliated with the W3C standards body.
</p>
<p>
Their published content is inaccurate and misleading.
</p>
<div class="source">
Further Reading: <a href="http://w3fools.com/">W3Fools</a>
</div>
</article>
<!-- MDN -->
<article>
<h3>W3Schools Alternatives</h3>
<img style="float: left; margin-top: 20px; margin-right: 10px;" src="img/mdn.png">
<p>
The <a href="https://developer.mozilla.org">Mozilla Developer Network</a> is a
comprehensive source of documentation for JavaScript/HTML/CSS/XML/SVG and more.
</p>
<p>
Prefix any search with "MDN" to get the Mozilla Developer page as the first hit.
</p>
<pre>
MDN vertical-align</pre>
</article>
<!-- Segue to Browser Basics -->
<article class="segue">
<h2>Browser Basics</h2>
</article>
<!-- How It Works -->
<article>
<h3>
How It Works
</h3>
<p>
After any page is loaded, browsers immediately start parsing HTML elements.
</p>
<ul>
<li>Scripts encountered are executed immediately</li>
<li>Mark-up is parsed and organized into the DOM Tree</li>
<li>CSS is parsed into buckets based on the selector</li>
</ul>
</article>
<!-- DOM and Render Trees -->
<article class='smaller'>
<h3>DOM and Render Trees</h3>
<p>
The DOM tree is the result of parsing the HTML that comes back from the network layer.
</p>
<p>
The DOM Tree is combined with the CSS to form the render tree. This is ultimately what is painted on-screen.
</p>
<p>
There is a 1:1 relationship between HTML elements and DOM elements. There is not a 1:1 relationship between DOM elements and render elements.
</p>
<div style='margin-top: 20px; display: inline-block; vertical-align: top'>
DOM tree
<ul class='tree'>
<li>
html
<ul>
<li>
head
<ul>
<li>title</li>
<li>style</li>
</ul>
</li>
<li>
body
<ul>
<li>h1</li>
<li>
div
<ul>
<li>span</li>
<li>img</li>
<li>a</li>
</ul>
</li>
<li>
div
<ul>
<li>text block</li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
</ul>
</div>
<div style="margin: 20px 70px; display: inline-block; vertical-align: top">
CSS
<code style="display: block; font-size: 20px;">span { display: none; }</code>
</div>
<div style="margin-top: 20px; display: inline-block; vertical-align: top">
Render tree
<ul class='tree'>
<li>
viewport
<ul>
<li>
scrolling area
<ul>
<li>h1 block</li>
<li>
div block
<ul>
<li>img block</li>
<li>a text block</li>
</ul>
</li>
<li>
div block
<ul>
<li>
text line
<ul>
<li>text block</li>
</ul>
</li>
<li>
text line
<ul>
<li>text block</li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
</ul>
</div>
</article>
<!-- Painting Flow -->
<article>
<h3>Painting</h3>
<img style="height: 66px; width: 600px; margin: 30px auto; display: block;" src='img/flow.png'>
<q style="font-size: 1em; line-height: 45px; margin-left: 75px; margin-right: 75px; margin-top: 0;">
For better user experience, the rendering engine will try to display contents on the screen as soon as possible. It will not wait until all HTML is parsed before starting to build and layout the render tree. Parts of the content will be parsed and displayed, while the process continues with the rest of the contents that keeps coming from the network.
</q>
<div class="source">Source: <a href="http://www.html5rocks.com/en/tutorials/internals/howbrowserswork">How Browsers Work</a></div>
</article>
<!-- Rendering Engine Order -->
<article>
<h3>Painting</h3>
<p>
The rendering engine paints the render tree elements in order based on the stacking context.
</p>
<p>
The stacking context encapsulates z-index, element flow, and position within the mark-up.
</p>
<p>
The stacking order within a context for a block renderer is:
</p>
<ul>
<li>background color</li>
<li>background image</li>
<li>border</li>
<li>children</li>
<li>outline</li>
</ul>
<div class="source">Source: <a href="http://www.html5rocks.com/en/tutorials/internals/howbrowserswork">How Browsers Work</a>, <a href="http://www.w3.org/TR/CSS21/zindex.html">W3C - Stacking contexts</a></div>
</article>
<!-- Desktop Tools for Debugging CSS -->
<article>
<h3>Tools for Debugging CSS</h3>
<p>All desktop browsers have built in developer tools.</p>
<p>Debugging CSS issues is more effectively done within those developer tools.</p>
<p style='color: #c34daa;'>Individual CSS rules may be toggled</p>
<p>Rules and classes may also be added</p>
<p>Element states may be set to debug more interesting cases</p>
<div class="button">
Push Me
</div>
</article>
<!-- Firefox 3D Render View -->
<article class='fill'>
<h3>Firefox 3D render view</h3>
<img src="img/firefox3d.png">
</article>
<!-- Segue to Selectors -->
<article class="segue">
<h2>Selectors</h2>
</article>
<!-- Basic Selector Primitives -->
<article>
<h3>Basic Selector Primitives</h3>
<p>Shorthand language for matching CSS rules to DOM elements</p>
<p>Some basic examples:</p>
<table>
<thead>
<tr>
<th>
Selector
</th>
<th>
Category
</th>
<th>
Matched elements
</th>
</tr>
</thead>
<tbody>
<tr>
<td class="noWrapping"><code>.myClass</code></td>
<td>Class</td>
<td>Match element with class <code>myClass</code></td>
</tr>
<tr>
<td class="noWrapping"><code>#myID</code></td>
<td>ID</td>
<td>Match element with ID <code>myID</code></td>
</tr>
<tr>
<td class="noWrapping"><code>span</code></td>
<td>Tag</td>
<td>Match all <code>span</code>s</td>
</tr>
<tr>
<td class="noWrapping"><code>*</code></td>
<td>Universal</td>
<td>Match all elements</td>
</tr>
</tbody>
</table>
<p style="font-size: 0.7em">
Rules are divided into categories based on the right-most portion of the selector.<br>More
on this later.
</p>
<div class="source">
Further Reading: <a href="https://developer.mozilla.org/En/CSS/Class_selectors">Class selectors</a>,
<a href="https://developer.mozilla.org/En/CSS/ID_selectors">ID selectors</a>,
<a href="https://developer.mozilla.org/en/CSS/Type_selectors">Type selectors</a>,
<a href="https://developer.mozilla.org/en/CSS/Universal_selectors">Universal selector</a>
</div>
</article>
<!-- Combining Primitives -->
<article>
<h3>Combining Primitives</h3>
<table>
<thead>
<tr>
<th>Selector</th>
<th>Matched elements</th>
</tr>
</thead>
<tbody>
<tr>
<td class="noWrapping"><code>div.myClass</code></td>
<td>All <code>div</code>s with the class <code>myClass</code></td>
</tr>
<tr>
<td class="noWrapping"><code>div.myClass,<br>a#myID,<br>span</code></td>
<td>All <code>div</code>s with the class <code>myClass</code> AND<br>the <code>a</code> with ID <code>myID</code> AND<br>all <code>span</code>s</td>
</tr>
<tr>
<td class="noWrapping"><code>div .myClass</code></td>
<td>Any element with class <code>myClass</code> which has an ancestor that is a <code>div</code></td>
</tr>
<tr>
<td class="noWrapping"><code>div > .myClass</code></td>
<td>Any element with class <code>myClass</code> whose parent is a <code>div</code></td>
</tr>
<tr>
<td class="noWrapping"><code>div + .myClass</code></td>
<td>Any element with class <code>myClass</code> that is immediately preceded by a <code>div</code></td>
</tr>
</tbody>
</table>
<div class="source">
Further Reading: <a href="https://developer.mozilla.org/en/CSS/Child_selectors">Child selectors</a>,
<a href="https://developer.mozilla.org/en/CSS/Descendant_selectors">Descendant selectors</a>
</div>
</article>
<!-- Attribute Selectors -->
<article>
<h3>Attribute Selectors</h3>
<table>
<thead>
<tr>
<th>Selector</th>
<th>Matched elements</th>
</tr>
</thead>
<tbody>
<tr>
<td class="noWrapping"><code>input[checked]</code></td>
<td>All checked <code>input</code>s</td>
</tr>
<tr>
<td class="noWrapping"><code>input[type='text']</code></td>
<td>All line edits</td>
</tr>
</tbody>
</table>
<div class="source">
Further Reading: <a href="https://developer.mozilla.org/en/CSS/Attribute_selectors">Attribute Selectors</a>
</div>
</article>
<!-- Pseudo Classes -->
<article>
<h3>Pseudo Classes</h3>
<p>CSS allows matching to special states of elements.</p>
<table>
<thead>
<tr>
<th>Selector</th>
<th>Matched elements</th>
</tr>
</thead>
<tbody>
<tr>
<td class="noWrapping"><code>a:link</code></td>
<td>All unvisited links</td>
</tr>
<tr>
<td class="noWrapping"><code>a:visited</code></td>
<td>All visited links</td>
</tr>
<tr>
<td class="noWrapping"><code>a:active</code></td>
<td>Matches a link that is being clicked on</td>
</tr>
<tr>
<td class="noWrapping"><code>*:focus</code></td>
<td>Matches the elements with the current focus</td>
</tr>
<tr>
<td class="noWrapping"><code>.myClass:hover</code></td>
<td>Matches when hovering over an element with class <code>myClass</code></td>
</tr>
</tbody>
</table>
<div class="source">
Further Reading: <a href="https://developer.mozilla.org/en/CSS/Pseudo-classes">Pseudo-Classes</a>
</div>
</article>
<!-- More Pseudo Classes -->
<article class="smaller">
<h3>More Pseudo Classes</h3>
<p>These selectors match elements very specific placement within the DOM</p>
<table>
<thead>
<tr>
<th>Selector</th>
<th>Matched elements</th>
</tr>
</thead>
<tbody>
<tr>
<td class="noWrapping"><code>li:first-child</code></td>
<td>Matches the first list item under the parent</td>
</tr>
<tr>
<td class="noWrapping"><code>div:nth-child(<em>a</em>n + <em>b</em>)</code></td>
<td>Matches <code>div</code>s that are <em>b</em>th child of the parent after all its children have been split into groups of <em>a</em> elements each.</td>
</tr>
<tr>
<td class="noWrapping"><code>span:nth-of-type(<em>a</em>n + <em>b</em>)</code></td>
<td>Similar to nth-child except the groups only contain <code>span</code>s</td>
</tr>
<tr>
<td class="noWrapping"><code>.myClass:empty</code></td>
<td>Matches elements with class <code>myClass</code> without any children<br><strong>Note:</strong> text (including whitespace) are considered children</td>
</tr>
<tr>
<td class="noWrapping"><code>input:enabled</code></td>
<td>Matches all enabled <code>input</code> fields</td>
</tr>
<tr>
<td class="noWrapping"><code>input:disabled</code></td>
<td>Matches all disabled <code>input</code> fields</td>
</tr>
<tr>
<td class="noWrapping"><code>span:not(.myClass)</code></td>
<td>Matches all <code>span</code>s without class <code>myClass</code></td>
</tr>
</tbody>
</table>
<div class="source">
Further Reading: <a href="https://developer.mozilla.org/en/CSS/Pseudo-classes">Pseudo-Classes</a>,
<a href="https://developer.mozilla.org/en/CSS/%3Anth-child">:nth-child</a>,
<a href="https://developer.mozilla.org/en/CSS/%3Anth-of-type">:nth-of-type</a>,
<a href="https://developer.mozilla.org/en/CSS/%3Aempty">:empty</a>,
<a href="https://developer.mozilla.org/en/CSS/%3Anot">:not</a>
</div>
</article>
<!-- Conflicting Styles -->
<article>
<h3>How Are Conflicting Styles Resolved?</h3>
<p>The rendering engine may have multiple styles it needs to apply to a particular element.</p>
<pre>div { background-color: green; }
div { background-color: gray; }</pre>
<div style="height: 100px; width: 600px; margin: 40px auto; position: relative">
<div style="width: 300px; height: 100%; background-color: green; display: inline-block;">
</div><div style="width: 300px; height: 100%; background-color: gray; display: inline-block;"></div>
<div style="position: absolute; left: 50%; top: 50%; margin-left: -267px; margin-top: -18px; color: black;">
Should the background be <span style="color: #adff2f;">green</span> or <span style="color: lightgray;">gray</span>?
</div>
</div>
</article>
<!-- Resolution Characteristics -->
<article>
<h3>Resolution Characteristics</h3>
<p>
Resolving conflicts requires looking at several pieces of information
</p>
<ul>
<li>Rule origin - Where did the rule originate?</li>
<li>Specificity - How specific is the rule?</li>
<li>Importance - Was the rule declared as <code>!important</code>?</li>
<li>Order - What order were the rules loaded?</li>
</ul>
<div class="source">
Further Reading: <a href="http://reference.sitepoint.com/css/cascade">The Cascade</a>
</div>
</article>
<!-- Resolution Steps -->
<article>
<h3>Resolution Steps</h3>
<p>
Resolving CSS properties is done in four steps
</p>
<ol>
<li>For a given property, find all declarations that apply to a specific element.</li>
<li>Sort the declarations according to their levels of importance, and origins.</li>
<li>Sort declarations with the same level of importance and origin by selector specificity.</li>
<li>Finally, if declarations have the same level of importance, origin, and specificity, sort them by the order in which they’re specified; the last declaration wins.</li>
</ol>
<div class="source">
Source: <a href="http://reference.sitepoint.com/css/cascade">The Cascade</a>
</div>
</article>
<!-- Rule Origin -->
<article>
<h3>Rule Origin</h3>
<p>
The origin of a CSS rule refers the stylesheet where it appears.
</p>
<p>
Rules are imported from three sources:
</p>
<table>
<tr>
<td>
User Agent
</td>
<td>
The default stylesheet for the device rendering the output. This is usually a web
browser but may be a phone, TV, or
<a href="http://media.photobucket.com/image/webos%20toaster/g_manq/webOSToaster.jpg">household appliance</a>.
</td>
</tr>
<tr>
<td>
User Stylesheet
</td>
<td>
Most desktop browsers allow users to provide their own
<a href="https://twitter.com/paul_irish/status/217303604254613504">custom defaults</a>
in the user stylesheet.
</td>
</tr>
<tr>
<td>
Author Stylesheet
</td>
<td>
Any rule imported via a <code>link</code> or <code>style</code> element or in an
element's <code>style</code> attribute.
</td>
</tr>
</table>
</article>
<!-- How Origin is Applied -->
<article>
<h3>How Origin is Applied</h3>
<p>
CSS rule declarations are sorted by origin in the following order from lowest to highest
</p>
<ol>
<li>User agent declarations</li>
<li>Normal declarations in user style sheets</li>
<li>Normal declarations in author style sheets</li>
<li>Important declarations in author style sheets</li>
<li>Important declarations in user style sheets</li>
</ol>
<div class="source">
Further Reading: <a href="http://reference.sitepoint.com/css/cascade">The Cascade</a>
</div>
</article>
<!-- Specificity -->
<article>
<h3>Specificity</h3>
<p>
More specific rules are applied over less specific ones. But how is specificity calculated?
</p>
<p>
Rules are split into 4 categories, a, b, c, d.
</p>
<ul>
<li><strong>a</strong> = 1 if the declaration is inline rather than on a selector, else <strong>a</strong> = 0</li>
<li><strong>b</strong> = the count of the number of ID attributes</li>
<li><strong>c</strong> = the count of other attributes (like class names) and pseudo-classes</li>
<li><strong>d</strong> = the count of element names and pseudo-elements</li>
</ul>
<p>
Concatenating the four counts (in a hex base) gives the specificity
</p>
<div class="source">
Source: <a href="http://www.html5rocks.com/en/tutorials/internals/howbrowserswork/#Specificity">Specificity</a>
</div>
</article>
<!-- Important -->
<article>
<h3>Use of !important</h3>
<p>
The <code>!important</code> directive can override other rules with less specificity.
</p>
<p>
This is akin to the <a href="http://en.wikipedia.org/wiki/Nuclear_option">nuclear option</a>.
</p>
<p>
Treat <code>!important</code> as a code smell.
</p>
</article>
<article>
<h3>Order</h3>
<p>
Understanding order is simple: Last always wins.
</p>
<pre>
<div style="background-color: red;
background-color: lightblue;">
Last always wins.
</div></pre>
<div style="background-color: green; background-color: lightblue; padding: 10px;">
Last always wins.
</div>
</article>
<!-- Segue to Units of Measurement -->
<article class="segue">
<h2>Units of Measurement</h2>
</article>
<!-- Introducing Font-Relative Lengths -->
<article>
<h3>Font-Relative Lengths</h3>
<q style="font-size: 1em; line-height: 45px; margin-left: 75px; margin-right: 75px; margin-top: 40px; text-align: justify;">
Aside from <code>rem</code> (which refers to the font-size of the root element), the font-relative
lengths refer to the computed font metrics of the element on which they are used. The
exception is when they occur in the value of the <code>font-size</code> property itself, in which
case they refer to the font metrics of the parent element (or the font metrics
corresponding to the initial values of the <code>font</code> property, if the element has no parent).
</q>
<div class="source">
Source: <a href="http://www.w3.org/TR/css3-values/#font-relative-lengths">Font-Relative Lengths</a>
</div>
</article>
<!-- Font-Relative Length Details -->
<article class="smaller">
<h3>Font Relative Lengths</h3>
<table>
<tr>
<td>
<code>1.0em</code>
</td>
<td>
Equal to the computed value of the <code>font-size</code>
</td>
</tr>
<tr>
<td>
<code>1.0ex</code>
</td>
<td>
Equal to the height of the lowercase "x"
</td>
</tr>
<tr>
<td>
<code>1.0ch</code>
</td>
<td>
Equal to the height of 0
</td>
</tr>
<tr>
<td>
<code>1.0rem</code>
</td>
<td>
Equal to the computed value of the <code>font-size</code> of the root element
</td>
</tr>
</table>
<pre>h1 { line-height: 1.2em; }</pre>
<p>
The line height of <code>h1</code> elements will be 20% greater than the font size of the <code>h1</code> element
</p>
<pre>h1 { font-size: 1.2em; }</pre>
<p>
The font-size of <code>h1</code> elements will be 20% greater than the inherited font size
</p>
<div class="source">
Source: <a href="http://www.w3.org/TR/css3-values/#font-relative-lengths">Font Relative Lengths</a>
</div>
</article>
<!-- Absolute Lengths -->
<article class="smaller">
<h3>Absolute Lengths</h3>
<q style="font-size: 1em; line-height: 45px; margin-left: 75px; margin-right: 75px; margin-top: 40px; text-align: justify;">
Absolute length units are fixed in relation to each other and anchored to some physical measurement.
</q>
<p>
Some common units of measurement:
</p>
<table>
<tr>
<td><code>cm</code></td>
<td>centimeters</td>
</tr>
<tr>
<td><code>in</code></td>
<td>inches - defined as 2.54cm</td>
</tr>
<tr>
<td><code>px</code></td>
<td>pixel - defined as 1/96th of an inch or the size of the device's reference pixel</td>
</tr>
<tr>
<td><code>pt</code></td>
<td>points - defined as 1/72nd of an inch</td>
</tr>
</table>
<p>
In practice, the best unit of measurement depends on the media.
</p>
<p>
Pixels make sense on screen. Centimeters and inches make sense in printed media.
</p>
<div class="source">
Source: <a href="http://www.w3.org/TR/css3-values/#absolute-lengths">Absolute Lengths</a>
</div>
</article>
<!-- Percentages -->
<article>
<h3>Percentages</h3>
<p>
Percentage values are always relative to some other value. Properties that allow
percentages implicitly define the value to which the percentage refers.
</p>
<pre>
<div style="height: 100px;">
<div style="height: 50%; width: 50%;">
50% as big as the parent
</div>
</div></pre>
<div class="box box1" style="height: 100px;">
<div class="box box2" style="height: 50%; width: 50%;">50% as big as the parent</div>
</div>
<div class="source">
Source: <a href="http://www.w3.org/TR/css3-values/#percentages">Percentages</a>
</div>
</article>
<!-- Viewport Relative Lengths -->
<article>
<h3>Viewport-Relative Units</h3>
<p>
CSS3 introduces viewport-relative units. These are supported in Chrome and IE.
</p>
<p>
Percentages are relative to a value on an ancestor element. Viewport-relative units
are always in relation to the viewport size.
</p>
<table>
<tr>
<td>
vh
</td>
<td>
1% of the viewport height
</td>
</tr>
<tr>
<td>
vw
</td>
<td>
1% of the viewport width
</td>
</tr>
<tr>
<td>
vm
</td>
<td>
The smaller of vh and vw
</td>
</tr>
</table>
<div class="box box1 exampleSpacing" style="width: 40vw; font-size: 20px;">
Viewport-relative unit supported this box is shorter than the slide width.
</div>
<div class="source">
Further Reading: <a href="http://css-tricks.com/viewport-sized-typography/">Viewport-Sized Typography</a>
</div>