The new book targets IT professionals and helps them get projects back on track using proven, real-world project management tools and techniques. Readers learn how to make an immediate impact on IT projects.

New Cisco Press Materials Forthcoming, Plus Special 40% Offer

Online Resource

Barker Library - TP1151.L37 S3613 2018

Hayden Library - TP155.5.C76 2019

Dewey Library - TP559.M53 M34 2019

Tverberg, Lois, author

Neville, David J., author

Beavis, Mary Ann, author

Bousset, Wilhelm, 1865-1920

Senior, Donald, author

Schaberg, Jane

Hall, Crystal L., author

Campbell, Joseph, 1904- author

Fox, Arminta M., author

Using CSS 2.1 pseudo-elements to provide up to 3 background canvases, 2 fixed-size presentational images, and multiple complex borders for a single HTML element. This method of progressive enhancement works for all browsers that support CSS 2.1 pseudo-elements and their positioning. No CSS3 support required.

• Demo: Multiple Backgrounds with CSS 2.1
• Demo: Multiple Borders with CSS 2.1

Support: Firefox 3.5+, Safari 4+, Chrome 4+, Opera 10+, IE8+.

How does it work?

Essentially, you create pseudo-elements using CSS (:before and :after) and treat them similarly to how you would treat HTML elements nested within your target element. But they have distinct benefits – beyond semantics – over the use of nested HTML elements.

To provide multiple backgrounds and/or borders, the pseudo-elements are pushed behind the content layer and pinned to the desired points of the HTML element using absolute positioning.

The pseudo-elements contain no true content and are absolutely positioned. This means that they can be stretched to sit over any area of the “parent” element without affecting its content. This can be done using any combination of values for the top, right, bottom, left, width, and height properties and is the key to their flexibility.

What effects can be achieved?

Using just one element you can create parallax effects, multiple background colours, multiple background images, clipped background images, image replacement, expandable boxes using images for borders, fluid faux columns, images existing outside the box, the appearance of multiple borders, and other popular effects that usually require images and/or the use of presentational HTML. It is also possible to include 2 extra presentational images as generated content.

The Multiple Backgrounds with CSS 2.1 and Multiple Borders with CSS 2.1 demo pages show how several popular examples of these effects can be achieved with this technique.

Most structural elements will contain child elements. Therefore, more often than not, you will be able to gain a further 2 pseudo-elements to use in the presentation by generating them from the first child (and even last-child) element of the parent element. In addition, you can use style changes on :hover to produce complex interaction effects.

Example code: multiple background images

Using this technique it is possible to reproduce multiple-background parallax effects like those found on the Silverback site using just one HTML element.

The element gets its own background image and any desired padding. By relatively positioning the element it acts as the reference point when absolutely positioning the pseudo-elements. The positive z-index will allow for the correct z-axis positioning of the pseudo-elements.

#silverback {
  position: relative;
  z-index: 1;
  min-width: 200px;
  min-height: 200px;
  padding: 120px 200px 50px;
  background: #d3ff99 url(vines-back.png) -10% 0 repeat-x;
}

Both pseudo-elements are absolutely positioned and pinned to each side of the element. The z-index value of -1 moves the pseudo-elements behind the content layer. This way the pseudo-elements sit on top of the element’s background and border but all the content is still selectable or clickable.

#silverback:before,
#silverback:after {
  position: absolute;
  z-index: -1;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  padding-top: 100px;
}

Each pseudo-element then has a repeated background-image set. This is all that is needed to reproduce the parallax effect.

The content property lets you add an image as generated content. With two pseudo-elements you can add 2 further images to an element. They can be crudely positioned within the pseudo-element box by varying other properties such as text-align and padding.

#silverback:before {
  content: url(gorilla-1.png);
  padding-left: 3%;
  text-align: left;
  background: transparent url(vines-mid.png) 300% 0 repeat-x;
}

#silverback:after {
  content: url(gorilla-2.png);
  padding-right: 3%;
  text-align: right;
  background: transparent url(vines-front.png) 70% 0 repeat-x;
}

The finished product is part of the Multiple Backgrounds with CSS 2.1 demo.

Example code: fluid faux columns

Another application is creating equal height fluid columns without images or extra nested containers.

The HTML base is very simple. I’ve used specific classes on each child div rather than relying on CSS 2.1 selectors that IE6 does not support. If you don’t require IE6 support you don’t actually need the classes.

<div id="faux">
  <div class="main">[content]</div>
  <div class="supp1">[content]</div>
  <div class="supp2">[content]</div>
</div>

The percentage-width container is once again relatively positioned and a positive z-index is set. Applying overflow:hidden gets the element to wrap its floated children and will hide the overflowing pseudo-elements. The background colour will provide the colour for one of the columns.

#faux {
  position: relative;
  z-index: 1;
  width: 80%;
  margin: 0 auto;
  overflow: hidden;
  background: #ffaf00;
}

By using relative positioning on the child div‘s you can also control the order of the columns independently of their source order.

#faux div {
  position: relative;
  float: left;
  width: 30%;
}

#faux .main { left: 35%; }
#faux .supp1 { left: -28.5%; }
#faux .supp2 { left: 8.5%; }

The other two full-height columns are produced by creating, sizing, and positioning pseudo-elements with backgrounds. These backgrounds can be (repeating) images if the design requires.

#faux:before,
#faux:after {
   content: "";
   position: absolute;
   z-index: -1;
   top: 0;
   right: 0;
   bottom: 0;
   left: 33.333%;
   background: #f9b6ff;
}

#faux:after {
   left: 66.667%;
   background: #79daff;
}

The finished product is part of the Multiple Backgrounds with CSS 2.1 demo.

Example code: multiple borders

Multiple borders are produced in much the same way. Using them can avoid the need for images to produce simple effects.

An element must be relatively positioned and have sufficient padding to contain the width of the extra border you will be creating with pseudo-elements.

#borders {
   position: relative;
   z-index: 1;
   padding: 30px;
   border: 5px solid #f00;
   background: #ff9600;
}

The pseudo-elements are positioned at specific distances away from the edge of the element’s box, moved behind the content layer with the negative z-index, and given the border and background values you want.

#borders:before {
   content: "";
   position: absolute;
   z-index: -1;
   top: 5px;
   left: 5px;
   right: 5px;
   bottom: 5px;
   border: 5px solid #ffea00;
   background: #4aa929;
}

#borders:after {
   content: "";
   position: absolute;
   z-index: -1;
   top: 15px;
   left: 15px;
   right: 15px;
   bottom: 15px;
   border: 5px solid #00b4ff;
   background: #fff;
}

That’s all there is to it. The finished product is part of the Multiple Borders with CSS 2.1 demo.

Progressive enhancement and legacy browsers

IE6 and IE7 have no support for CSS 2.1 pseudo-elements and will ignore all :before and :after declarations. They get none of the enhancements but are left with the basic usable experience.

A warning about Firefox 3.0

Firefox 3.0 supports CSS 2.1 pseudo-elements but does not support their positioning. Due to this partial support, you should avoid declaring display:block for absolutely positioned pseudo-elements that explicitly declare a width or height values. However, when using borders there is no graceful fallback for Firefox 3.0. Although, sometimes an improved appearance in Firefox 3.0 can be achieved by adding display:block to pseudo-element hacks that use borders.

Enhancing with CSS3

All the applications included in this article could be further enhanced to take advantage of present-day CSS3 implementations.

Using border-radius, rgba, and transforms, and CSS3 multiple background images in tandem with pseudo-elements can produce even more complex presentations that I hope to include in a future article. Currently there is no browser support for the use of CSS3 transitions or animations on pseudo-elements.

In the future: CSS3 pseudo-elements

The proposed extensions to pseudo-elements in the CSS3 Generated and Replaced Content Module include the addition of nested pseudo-elements (::before::before), multiple pseudo-elements (::after(2)), wrapping pseudo-elements (::outside), and the ability to insert pseudo-elements into later parts of the document (::alternate).

These changes would provide a near limitless number, and arrangement, of pseudo-elements for all sorts of complex effects and presentations using just one element.

Let me know what you’ve done

I’ve focused on just a few applications and popular effects. If you find other applications, limitations, or want to share how you’ve applied this technique please leave a comment below or let me know on Twitter (@necolas.

Translations

• 使用css2.1实现多重背景、多重边框效果

Drop-shadows are easy enough to create using pseudo-elements. It’s a nice and robust way to progressively enhance a design. This post is a summary of the technique and some of the possible appearances.

Demo: CSS drop-shadows without images

Known support: Firefox 3.5+, Chrome 5+, Safari 5+, Opera 10.6+, IE 9+

I’ll be looking mainly at a few details involved in making this effect more robust. Divya Manian covered the basic principle in her article Drop Shadows with CSS3 and Matt Hamm recently shared his Pure CSS3 box-shadow page curl effect.

After a bit of back-and-forth on Twitter with Simurai, and proposing a couple of additions to Divya’s and Matt’s demos using jsbin, I felt like documenting and explaining the parts that make up this technique.

The basic technique

There is no need for extra markup, the effect can be applied to a single element. A couple of pseudo-elements are generated from an element and then pushed behind it.

.drop-shadow {
  position: relative;
  width: 90%;
}

.drop-shadow:before,
.drop-shadow:after {
  content: "";
  position: absolute;
  z-index: -1;
}

The pseudo-elements need to be positioned and given explicit or implicit dimensions.

.drop-shadow:before,
.drop-shadow:after {
  content: "";
  position: absolute;
  z-index: -1;
  bottom: 15px;
  left: 10px;
  width: 50%;
  height: 20%;
}

The next step is to add a CSS3 box-shadow and apply CSS3 transforms. Different types of drop-shadow can be produced by varying these values and the types of transforms applied.

.drop-shadow:before,
.drop-shadow:after {
  content: "";
  position: absolute;
  z-index: -1;
  bottom: 15px;
  left: 10px;
  width: 50%;
  height: 20%;
  box-shadow: 0 15px 10px rgba(0, 0, 0, 0.7);
  transform: rotate(-3deg);
}

One of the pseudo-elements then needs to be positioned on the other side of the element and rotated in the opposite direction. This is easily done by overriding only the properties that need to differ.

.drop-shadow:after{
  right: 10px;
  left: auto;
  transform: rotate(3deg);
 }

The final core code is as shown below. There is just one more addition – max-width – to prevent the drop-shadow from extending too far below very wide elements.

.drop-shadow {
  position: relative;
  width: 90%;
}

.drop-shadow:before,
.drop-shadow:after {
  content: "";
  position: absolute;
  z-index: -1;
  bottom: 15px;
  left: 10px;
  width: 50%;
  height: 20%;
  max-width: 300px;
  box-shadow :0 15px 10px rgba(0, 0, 0, 0.7);
  transform: rotate(-3deg);
}

.drop-shadow:after{
  right: 10px;
  left: auto;
  transform: rotate(3deg);
}

No Firefox 3.0 problems this time

Some pseudo-element hacks require a work-around to avoid looking broken in Firefox 3.0 because that browser does not support the positioning of pseudo-elements. This usually involves implicitly setting their dimensions using offsets.

However, as Divya Manian pointed out to me, in this case we’re only using box-shadow – which Firefox 3.0 doesn’t support – and Firefox 3.0 will ignore the position:absolute declaration for the pseudo-elements. This leaves them with the default display:inline style. As a result, there is no problem explicitly setting the pseudo-element width and height because it won’t be applied to the pseudo-elements in Firefox 3.0.

Further enhancements

From this base there are plenty of ways to tweak the effect by applying skew to the pseudo-elements and modifying the styles of the element itself. A great example of this was shared by Simurai. By adding a border-radius to the element you can give the appearance of page curl.

.drop-shadow {
  border-radius: 0 0 120px 120px / 0 0 6px 6px;
}

I’ve put together a little demo page with a few of drop-shadow effects, including those that build on the work of Divya Manian and Matt Hamm.

If you’ve got your own improvements, please send them to me on Twitter.

I’ve started using a backup strategy based on that originally described by Jamie Zawinski and subsequently covered in Jeff Atwood’s What’s your backup strategy? article. It works by incrementally backing up your data to a bootable clone of your computer’s internal drive, in order to replace the internal drive when it fails.

This script is maintained in my dotfiles repo. Please report problems or improvements in the issue tracker.

This post is mainly to document – for myself as much as anything – the process I went through in order to implement an incremental backup strategy in OS X 10.6+. Use at your own risk. Feel free to suggest improvements if you know of any.

Formatting and partitioning the drive

With your backup drive in its enclosure, connect the drive to your Mac and open the Disk Utility application.

1. Click on the disk’s name. This should bring up a “Partition” tab in the right panel.
2. Click on the “Partition” tab.
3. Under “Volume scheme” select the number of partitions you need. Probably “1 partition” if it is to match your internal disk.
4. Under “Name” enter the volume name you want to use, e.g., “Backup”.
5. Under “Format” select “Mac OS X Extended (Journaled)”, which is necessary if the disk is to be bootable.
6. Click “Options” and check that “GUID Partition Table” is selected.
7. Click “Apply”.

This will format and partition the disk. The partition(s) should now show up in the Finder and on the Desktop.

Enable ownership permissions

The new partition needs permissions to be enabled to avoid chown errors when using rsync. To do this, select the partition and view its information page (using “Get Info” or Command+I). Expand the “Ownership & Permissions” section and uncheck “Ignore ownership on this volume”

Backup script

The backup script uses rsync – a fast and versatile file copying tool – to manage the copying and moving of data between volumes. You need to install rsync 3 (this is easily done using Homebrew: brew install https://raw.github.com/Homebrew/homebrew-dupes/master/rsync.rb). Rsync offers a wide variety of options and only copies the differences between the source files and the existing files in the destination, making it ideal for incremental backups. You can find out more about rsync in the rsync documentation

The following is the contents of a script I’ve named backup. I’m using it to backup all of the data on my internal disk, with a specified set of exceptions contained within a file called .backupignore.

#!/bin/bash

# Disc backup script
# Requires rsync 3

# Ask for the administrator password upfront
sudo -v

# IMPORTANT: Make sure you update the `DST` variable to match the name of the
# destination backup drive

DST="/Volumes/Macintosh HD/"
SRC="/"
EXCLUDE="$HOME/.backupignore"

PROG=$0

# --acls                   update the destination ACLs to be the same as the source ACLs
# --archive                turn on archive mode (recursive copy + retain attributes)
# --delete                 delete any files that have been deleted locally
# --delete-excluded        delete any files (on DST) that are part of the list of excluded files
# --exclude-from           reference a list of files to exclude
# --hard-links             preserve hard-links
# --one-file-system        don't cross device boundaries (ignore mounted volumes)
# --sparse                 handle sparse files efficiently
# --verbose                increase verbosity
# --xattrs                 update the remote extended attributes to be the same as the local ones

if [ ! -r "$SRC" ]; then
    logger -t $PROG "Source $SRC not readable - Cannot start the sync process"
    exit;
fi

if [ ! -w "$DST" ]; then
    logger -t $PROG "Destination $DST not writeable - Cannot start the sync process"
    exit;
fi

logger -t $PROG "Start rsync"

sudo rsync --acls 
           --archive 
           --delete 
           --delete-excluded 
           --exclude-from=$EXCLUDE 
           --hard-links 
           --one-file-system 
           --sparse 
           --verbose 
           --xattrs 
           "$SRC" "$DST"

logger -t $PROG "End rsync"

# Make the backup bootable
sudo bless -folder "$DST"/System/Library/CoreServices

exit 0

Adapted from the rsync script at Automated OSX backups with launchd and rsync

This is the contents of the .backupignore file.

.Spotlight-*/
.Trashes
/afs/*
/automount/*
/cores/*
/dev/*
/Network/*
/private/tmp/*
/private/var/run/*
/private/var/spool/postfix/*
/private/var/vm/*
/Previous Systems.localized
/tmp/*
/Volumes/*
*/.Trash

Adapted from the excludes file at Automated OSX backups with launchd and rsync

Every time the script runs, messages will be written to the system log.

Check that the source (SRC) and destination (DST) paths in the script are correct and match the volume name that you chose when partitioning the disk. Wrapping the $SRC and $DST variables in double quotes ensures that the script will work even if your volume names contain spaces (e.g. “Macintosh Backup”).

The command option --exclude-from tells the script where to find the file containing the exclude patterns. Make sure you either have .backupignore in the home directory or that you update this part of the command to reference the full path of the excludes file.

Running the backup script

You can run the script from the command line, or make it executable from the Finder or the Desktop:

1. Type the following into the command line to ensure that you have permission to execute the script:

   chmod +x /path/to/rsync_backup.sh
   

2. Remove the .sh extension from the script.

3. Create an alias of the script and move it to the Desktop.
4. Double click the icon to run the backup script.

It’s important to run the script regularly in order to keep the backup in sync with your internal disk. If you have a desktop computer, or you never turn off your laptop, you can automate the running of the script by setting up a cron job.

Checking the disk is bootable

Once you’ve run the backup script, you should test that the backup disk is bootable. To do this, restart your computer and hold down the Alt/Option key. Your backup disk should be presented, with the volume name you chose, as a bootable disk.

When I first booted my backup, the terminal displayed the following line:

dyld: shared cached file was build against a different libSystem.dylib, ignoring cache

According to this article, the fix for this is to update the cache by entering the following into the terminal:

sudo update_dyld_shared_cache -force

That should be everything you need to start implementing an incremental backup strategy when using OS X.

Taking a “mobile first” approach to web development poses some challenges if you need to provide a “desktop” experience for legacy versions of IE. Using a CSS pre-processor like Sass can help.

As of Sass 3.2, there is another way of catering for IE, described by Jake Archibald.

One aspect of a “mobile first” approach to development is that your styles are usually gradually built up from a simple base. Each new “layer” of CSS adds presentational adjustments and complexity, via CSS3 Media Queries, to react to and make use of additional viewport space. However, IE 6/7/8 do not support CSS3 Media Queries. If you want to serve IE 6/7/8 something more than just the base CSS, then you need a solution that exposes the “enhancing” CSS to those browsers.

Popular existing options

An existing option is the use of a CSS3 Media Query polyfill, such as Respond.js. However, there are some drawbacks to this approach (see the project README), such as the introduction of a JavaScript dependency and the XHRing of your style sheets, which may introduce performance or cross-domain security issues. Furthermore, adding support for CSS3 Media Queries is probably not necessary for these legacy browsers. The main concern is exposing the “enhancing” CSS.

Another method, which Jeremy Keith has described in his post on Windows mobile media queries, is to use separate CSS files: one basic global file, and an “enhancing” file that is referenced twice in the <head> of the document. The “enhancing” file is referenced once using a media attribute containing a CSS3 Media Query value. This prevents it being downloaded by browsers (such as IE 6/7/8) which do not support CSS3 Media Queries. The same file is then referenced again, this time wrapped in an IE conditional comment (without the use of a CSS3 Media Query value) to hide it from modern browsers. However, this approach becomes somewhat cumbersome, and introduces multiple HTTP requests, if you have multiple breakpoints in your responsive design.

Getting Sass to help

Sass 3.1 provides some features that help make this second approach more flexible. The general advantages of the Sass-based approach I’ve used are:

1. You have full control over how your style sheets are broken up and reassembled.
2. It removes the performance concerns of having to reference several separate style sheets for each breakpoint in the responsive design, simply to cater for IE 6/7/8.
3. You can easily repeat large chunks of CSS in separate compiled files without introducing maintenance problems.

The basic idea is to produce two versions of your compiled CSS from the same core code. One version of your CSS includes CSS3 @media queries and is downloaded by modern browsers. The other version is only downloaded by IE 6/7/8 in a desktop environment and contains no CSS3 @media queries.

To do this, you take advantage of the fact that Sass can import and compile separate .scss/.sass files into a single CSS file. This allows you to keep the CSS rules used at any breakpoint completely separate from the @media query that you might want it to be a part of.

This is not a CSS3 Media Query polyfill, so one assumption is that IE 6/7/8 users will predominantly be using mid-size screens and should receive styles appropriate to that environment. Therefore, in the example below, I am making a subjective judgement by including all the breakpoint styles up to a width of 960px but withholding those for any breakpoints beyond that.

The ie.scss file imports numerous other files, each containing a layer of CSS that builds upon the previous each layer of CSS. No CSS3 @media queries are contained within the files or the ie.scss file. It then compiles to a single CSS file that is designed to be served only to IE 6/7/8.

// ie.scss

@import "base";
@import "320-up";
@import "480-up";
@import "780-up";
@import "960-up";

The style.scss file imports the code for each breakpoint involved in the design (including any beyond the limit imposed for legacy versions of IE) but nests them within the relevant CSS3 @media query. The compiled version of this file is served to all browsers apart from IE 6/7/8 and IEMobile.

// style.scss

@import "base";
@media (min-width:320px) {
    @import "320-up"; }
@media (min-width:480px) {
    @import "480-up"; }
@media (min-width:780px) {
    @import "780-up"; }
@media (min-width:960px) {
    @import "960-up"; }
@media (min-width:1100px) {
    @import "1100-up"; }

The resulting CSS files can then be referenced in the HTML. It is important to hide the ie.css file from any IE-based mobile browsers. This ensures that they do not download the CSS meant for desktop versions of IE.

<!--[if (gt IE 8) | (IEMobile)]><!-->
<link rel="stylesheet" href="/css/style.css">
<!--<![endif]-->

<!--[if (lt IE 9) & (!IEMobile)]>
<link rel="stylesheet" href="/css/ie.css">
<![endif]-->

This Sass-enabled approach works just as well if you need to serve a basic style sheet for mobiles without CSS3 Media Query support, and prevent those devices from downloading the CSS used to adapt the layout to wider viewports. For example, you can avoid importing base.scss into the ie.scss and style.scss files. It can then be referenced separately in the HTML.

<link rel="stylesheet" href="/css/base.css">
<link rel="stylesheet" href="/css/style.css" media="(min-width:320px)">

<!--[if (lt IE 9) & (!IEMobile)]>
<link rel="stylesheet" href="/css/ie.css">
<![endif]-->

You’ll notice that I didn’t wrap the style.css reference in a conditional comment to hide it from legacy versions of IE. It’s not necessary this time because the value of the media attribute is not understood by legacy versions of IE, and the style sheet will not be downloaded.

In different circumstances, different combinations of style sheets and media attribute values will be more appropriate.

Summary

Even if you want to don’t want to use any of the Sass or SCSS syntax, the pre-processor itself can help you to write your CSS in a “mobile first” manner (with multiple breakpoints), provide a “desktop” experience for IE 6/7/8, and avoid some of the performance or maintenance concerns that are sometimes present when juggling the two requirements.

I’m relatively new to using Sass, so there may be even better ways to achieve the same result or even to prevent the inclusion of IE-specific CSS unless the file is being compiled into a style sheet that only IE will download.

Bhopal, by comparison, has so far reported 679 cases and 24 deaths, with 354 patients, or more than half of those infected, having recovered.