Everyone loves motion. Adding the fourth dimension (time) to a site design is the main way screen-based design stands out from print design. CSS Transitions are a simple method for animating properties of an element enabling you to enrich certain events in your web design, without the need of Flash or JavaScript.
The W3C aptly describes transitions on their website as “CSS Transitions allows property changes in CSS values to occur smoothly over a specified duration”. In other words, CSS transitions allow us to modify a property incrementally, creating a sensation of motion and imbuing designs with subtlety and emotion that isn’t possible with a quick change.
Browser support
All modern browsers (yes even IE!) now support CSS transitions. However, importantly, if transitions aren’t supported in the browser being used, the transition is ignored and the property changes will be applied instantly. This graceful degradation is a cornerstone of best practice.
In order to extend the range of browser support we can use vendor prefixes, this extends the feature to include Firefox 4–15, Opera 10.5–12 and most versions of Chrome and Safari. The code, including the vendor prefix alternatives looks like this:
div { -o-transition: all 1s ease; -moz-transition: all 1s ease; -webkit-transition: all 1s ease; transition: all 1s ease; }
The non-prefixed property is added at the bottom of the stack to ensure final implemantation will trump all the others, as the property moves from draft to finished status.
Transition parameters
There are four parameters for CSS transitions:
- transition-property: the property to be tweened, or the keyword ‘all’ to apply to all properties;
- transition-duration: the duration of the transition;
- transition-timing-function: the easing to be applied, this creates more natural looking movement
- transtion-delay: specifies a delay to the start of the transition.
In addition, you can also use the shorthand property (as in the example above) where the parameters are specified as property, duration, timing function, delay.
Properties that can be transitioned
You can only transition properties that can be translated into a mathematical value. So for example, you can transition font-size; you cannot transition font-face.
The full list of properties that can currently be transitioned is as follows:
background-position, border-bottom-color, border-bottom-width, border-left-color, border-left-width, border-right-color, border-right-width, border-spacing, border-top-color, border-top-width, bottom, clip, color, font-size, font-weight, height, left, letter-spacing, margin-bottom, margin-left, margin-right, margin-top, max-height, max-width, min-height, min-width, opacity, outline-color, outline-width, padding-bottom, padding-left, padding-right, padding-top, right, text-indent, text-shadow, top, vertical-align, width, word-spacing, z-index.
Using transitions
Transition declarations are attached to the normal state of the element. Therefore only declared once for several states such as :focus, :active and pseudo classes.
Using the following code we can set up a basic menu and a paragraph of text. It is styled so that the menu items change their color and background color when rolled over, and so that the inline link changes its underline color from white to green when hovered over:
<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8" /> <title>CSS transition demo</title> <style type='text/css'> /* STATIC PROPERTIES */ body {background:#fff; } ul { padding:0; margin:20px; } li { display:inline; padding:5px 0; } .nav a { padding:5px; } p { padding:0; margin:21px; } a { text-decoration:none; } /* PROPERTIES TO TWEEN */ .nav a { color:#bee0bf; background:#1a9e5c; } .nav a:hover { color:#fff; background:#38b476; } p a { color:#3fa32d; border-bottom:1px solid #fff; } p a:hover { color:#bee0bf; border-bottom:1px solid #3fa32d; } </style> </head> <body> <ul class='nav'> <li><a href='#'>Business</a></li> <li><a href='#'>Code</a></li> <li><a href='#'>Design</a></li> <li><a href='#'>Inspiration</a></li> <li><a href='#'>Miscellaneous</a></li> <li><a href='#'>Mobile</a></li> <li><a href='#'>News</a></li> <li><a href='#'>Resources</a></li> <li><a href='#'>Usability</a></li> </ul> <p>Integer posuere erat a ante <a href='#'>inline link</a> venenatis dapibus posuere velit aliquet. Nullam id dolor id nibh ultricies vehicula ut id elit. Integer posuere erat a ante venenatis dapibus posuere velit aliquet. Nullam quis risus eget urna mollis ornare vel eu leo.</p> </body> </html>
Here’s how it looks:
We want to tween those properties, to make them run smoothly. We want to tween both the color, and the background-color of the nav elements, but for the inline text, we only want to tween the underline. We do this by adding the following to our style definition:
/* CSS TRANSITIONS */ .nav a { -o-transition: all 500ms; -moz-transition: all 500ms; -webkit-transition: all 500ms; transition: all 500ms; } p a { -o-transition: border-bottom 250ms; -moz-transition: border-bottom 250ms; -webkit-transition: border-bottom 250ms; transition: border-bottom 250ms; }
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