a {
display: block;
background: url(sprite.png) no-repeat;
height: 30px;
width: 250px;
}
a:hover {
background-position: 0 -30px;
}The set height and width ensure only a portion of the sprite.png graphic is shown. The rollover shifts the position of the background image, revealing a different area of the graphic.
<link rel="stylesheet" type="text/css" href="print.css" media="print">| all | Used for all media type devices |
| aural | Used for speech and sound synthesizers |
| braille | Used for braille tactile feedback devices |
| embossed | Used for paged braille printers |
| handheld | Used for small or handheld devices |
| Used for printers | |
| projection | Used for projected presentations, like slides |
| screen | Used for computer screens |
| tty | Used for media using a fixed-pitch character grid, like teletypes and terminals |
| tv | Used for television-type devices |
html {
width:100%;
height:100%;
background:url(logo.png) center center no-repeat;
}img {
position: absolute;
top: 50%;
left: 50%;
width: 500px;
height: 500px;
margin-top: -250px; /* Half the height */
margin-left: -250px; /* Half the width */
}html, body, #wrapper {
height:100%;
width: 100%;
margin: 0;
padding: 0;
border: 0;
}
#wrapper td {
vertical-align: middle;
text-align: center;
}<html>
<body>
<table id="wrapper">
<tr>
<td><img src="logo.png" alt="" /></td>
</tr>
</table>
</body>
</html>
The Flexbox Layout (Flexible Box) module (currently a W3C Candidate Recommandation) aims at providing a more efficient way to lay out, align and distribute space among items in a container, even when their size is unknown and/or dynamic (thus the word "flex").
The main idea behind the flex layout is to give the container the ability to alter its items' width/height (and order) to best fill the available space (mostly to accomodate to all kind of display devices and screen sizes). A flex container expands items to fill available free space, or shrinks them to prevent overflow.
Most importantly, the flexbox layout is direction-agnostic as opposed to the regular layouts (block which is vertically-based and inline which is horizontally-based). While those work well for pages, they lack flexibility (no pun intended) to support large or complex applications (especially when it comes to orientation changing, resizing, stretching, shrinking, etc.).
Note: Flexbox layout is most appropriate to the components of an application, and small-scale layouts, while the Grid layout is intended for larger scale layouts.
Since flexbox is a whole module and not a single property, it involves a lot of things including its whole set of properties. Some of them are meant to be set on the container (parent element, known as "flex container") whereas the others are meant to be set on the children (said "flex items").
If regular layout is based on both block and inline flow directions, the flex layout is based on "flex-flow directions". Please have a look at this figure from the specification, explaining the main idea behind the flex layout.
Basically, items will be layed out following either the main axis (from main-start to main-end) or the cross axis (from cross-start to cross-end).
flex-direction property (see below).
main-start | main-end - The flex items are placed within the container starting from main-start and going to main-end.
main size - A flex item's width or height, whichever is in the main dimension, is the item's main size. The flex item's main size property is either the ‘width’ or ‘height’ property, whichever is in the main dimension.
cross axis - The axis perpendicular to the main axis is called the cross axis. Its direction depends on the main axis direction.
cross-start | cross-end - Flex lines are filled with items and placed into the container starting on the cross-start side of the flex container and going toward the cross-end side.
cross size - The width or height of a flex item, whichever is in the cross dimension, is the item's cross size. The cross size property is whichever of ‘width’ or ‘height’ that is in the cross dimension.
This defines a flex container; inline or block depending on the given value. Thus, it enables a flex context for all its direct children.
display: other values | flex | inline-flex;Please note that:
CSS columns have no effect on a flex containerfloat, clear and vertical-align have no effect on a flex item
This establishes the main-axis, thus defining the direction flex items are placed in the flex container.
flex-direction: row | row-reverse | column | column-reverserow (default): left to right in ltr; right to left in rtl
row-reverse: right to left in ltr; left to right in rtl
column: aligns the flex items top to bottom
column-reverse: aligns the flex items bottom to top
This defines whether the flex container is single-line or multi-line, and the direction of the cross-axis, which determines the direction new lines are stacked in.
flex-wrap: nowrap | wrap | wrap-reversenowrap (default): single-line / left to right in ltr; right to left in rtl
wrap: multi-line / left to right in ltr; right to left in rtl
wrap-reverse: multi-line / right to left in ltr; left to right in rtl
This is a shorthand `flex-direction` and `flex-wrap` properties, which together define the flex container's main and cross axes. Default is `row nowrap`;
flex-flow: <‘flex-direction’> || <‘flex-wrap’>This defines the alignment along the main axis. It helps distribute extra free space leftover when either all the flex items on a line are inflexible, or are flexible but have reached their maximum size. It also exerts some control over the alignment of items when they overflow the line.
justify-content: flex-start | flex-end | center | space-between | space-aroundflex-start (default): items are packed toward the start line
flex-end: items are packed toward to end line
center: items are centered along the line
space-between: items are evenly distributed in the line; first item is on the start line, last item on the end line
space-around: items are evenly distributed in the line with equal space around them
This defines the default behaviour for how flex items are laid out along the cross axis on the current line. Think of it as the justify-content version for the cross-axis (perpendicular to the main-axis).
align-items: flex-start | flex-end | center | baseline | stretchflex-start: cross-start margin edge of the items is placed on the cross-start line
flex-end: cross-end margin edge of the items is placed on the cross-end line
center: items are centered in the cross-axis
baseline: items are aligned such as their baselines align
stretch (default): stretch to fill the container (still respect min-width/max-width)
This aligns a flex container's lines within when there is extra space in the cross-axis, similar to how justify-content aligns individual items within the main-axis.
Note: this property has no effect when the flexbox has only a single line.
align-content: flex-start | flex-end | center | space-between | space-around | stretchflex-start: lines packed to the start of the container
flex-end: lines packed to the end of the container
center: lines packed to the center of the container
space-between: lines evenly distributed; the first line is at the start of the container while the last one is at the end
space-around: lines evenly distributed with equal space between them
stretch (default): lines stretch to take up the remaining space
By default, flex items are layed out in the source order. However, the order property controls the order in which they appear in their container.
order: <integer>This defines the ability for a flex item to grow if necessary. It accepts a unitless value that serves as a proportion. It dictates what amount of the available space inside the flex container the item should take up.
If all items have flex-grow set to 1, every child will set to an equal size inside the container. If you were to give one of the children a value of 2, that child would take up twice as much space as the others.
flex-grow: <number> (default 0)Negative numbers are invalid.
This defines the ability for a flex item to shrink if necessary.
flex-shrink: <number> (default 1)Negative numbers are invalid.
This defines the default size of an element before the remaining space is distributed.
flex-basis: <length> | auto (default auto)This is the shorthand for flex-grow, flex-shrink and flex-basis. The second and third parameters (flex-shrink, flex-basis) are optional. Default is 0 1 auto.
flex: none | [ <'flex-grow'> <'flex-shrink'>? || <'flex-basis'> ]This allows the default alignment or the one specified by align-items to be overridden for individual flex items.
Please see the align-items explanation to understand the available values.
align-self: auto | flex-start | flex-end | center | baseline | stretchLet's start with a very very simple example, solving an almost daily problem: perfect centering. It couldn't be any simpler if you use flexbox.
.parent {
display: flex;
height: 300px; /* Or whatever */
}
.child {
width: 100px; /* Or whatever */
height: 100px; /* Or whatever */
margin: auto; /* Magic! */
}This relies on the fact a margin set to `auto` in a flex container absorb extra space. So setting a vertical margin of auto will make the item perfectly centered in both axis.
Now let's use some more properties. Consider a list of 6 items, all with a fixed dimensions in a matter of aesthetics but they could be auto-sized. We want them to be evenly and nicely distributed on the horizontal axis so that when we resize the browser, everything is fine (without media queries!).
.flex-container {
/* We first create a flex layout context */
display: flex;
/* Then we define the flow direction and if we allow the items to wrap
* Remember this is the same as:
* flex-direction: row;
* flex-wrap: wrap;
*/
flex-flow: row wrap;
/* Then we define how is distributed the remaining space */
justify-content: space-around;
}Done. Everything else is just some styling concern. Below is a pen featuring this example. Be sure to go to CodePen and try resizing your windows to see what happen.
Let's try something else. Imagine we have a right-aligned navigation on the very top of our website, but we want it to be centered on medium-sized screens and single-columned on small devices. Easy enough.
/* Large */
.navigation {
display: flex;
flex-flow: row wrap;
/* This aligns items to the end line on main-axis */
justify-content: flex-end;
}
/* Medium screens */
@media all and (max-width: 800px) {
.navigation {
/* When on medium sized screens, we center it by evenly distributing empty space around items */
justify-content: space-around;
}
}
/* Small screens */
@media all and (max-width: 500px) {
.navigation {
/* On small screens, we are no longer using row direction but column */
flex-direction: column;
}
}Let's try something even better by playing with flex items flexibility! What about a mobile-first 3-columns layout with full-width header and footer. And independent from source order.
.wrapper {
display: flex;
flex-flow: row wrap;
}
/* We tell all items to be 100% width */
.header, .main, .nav, .aside, .footer {
flex: 1 100%;
}
/* We rely on source order for mobile-first approach
* in this case:
* 1. header
* 2. nav
* 3. main
* 4. aside
* 5. footer
*/
/* Medium screens */
@media all and (min-width: 600px) {
/* We tell both sidebars to share a row */
.aside { flex: 1 auto; }
}
/* Large screens */
@media all and (min-width: 800px) {
/* We invert order of first sidebar and main
* And tell the main element to take twice as much width as the other two sidebars
*/
.main { flex: 2 0px; }
.aside-1 { order: 1; }
.main { order: 2; }
.aside-2 { order: 3; }
.footer { order: 4; }
}display: flex;)
(hybrid) means an odd unofficial syntax from 2011 (e.g. display: flexbox;)
(old) means the old syntax from 2009 (e.g. display: box;)
| 21+ (modern) 20- (old) |
3.1+ (old) | 2-21 (old) 22+ (new) |
12.1+ (modern) | 10+ (hybrid) | 2.1+ (old) | 3.2+ (old) |
Blackberry browser 10+ supports the new syntax.
For more informations about how to mix syntaxes in order to get the best browser support, please refer to this article (CSS-Tricks) or this article (DevOpera).
A Sass @mixin to help ease the pain:
@mixin flexbox() {
display: -webkit-box;
display: -moz-box;
display: -ms-flexbox;
display: -webkit-flex;
display: flex;
}
@mixin flex($values) {
-webkit-box-flex: $values;
-moz-box-flex: $values;
-webkit-flex: $values;
-ms-flex: $values;
flex: $values;
}
@mixin order($val) {
-webkit-box-ordinal-group: $val;
-moz-box-ordinal-group: $val;
-ms-flex-order: $val;
-webkit-order: $val;
order: $val;
}
.wrapper {
@include flexbox();
}
.item {
@include flex(1 200px);
@include order(2);
}
.stitched {
padding: 20px;
margin: 10px;
background: #ff0030;
color: #fff;
font-size: 21px;
font-weight: bold;
line-height: 1.3em;
border: 2px dashed #fff;
border-radius: 10px;
box-shadow: 0 0 0 4px #ff0030, 2px 1px 6px 4px rgba(10, 10, 0, 0.5);
text-shadow: -1px -1px #aa3030;
font-weight: normal;
}
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<title>Page Title</title>
<link rel="stylesheet" href="style.css" type="text/css" media="screen" charset="utf-8"/>
</head>
<body>
</body>
</html>
Firefox likes to assume when you click on a link to an RSS feed that you want to subscribe to it in some fashion. That might be true most of the time, but sometimes you just want to see the source of the RSS.
To view the source of an RSS feed, just append "view-source:" in the address bar before the feed address, like this:
view-source:http://today.wisc.edu/events/tag/humanities.rss