The transitions can be used to animate the CSS properties, adding an animation effect when changing CSS property of a HTML element, to gradually change from one style to another.
The CSS3 transition has 4 components:

To use CSS3 transition, you must specify two things:
      1. The CSS property you want to add an effect to ( transition-property ).
      2. The duration of the effect ( transition-duration ).
- The last two components ( transition-timing-function and transition-delay ) are optional.
- Internet Explorer supports CSS3 transition starting with IE 10.

Example. When a user mouse-over a Div, changes gradually its width.
<style type="text/css"> 
#iddv {
 transition-property: width;  
 transition-duration: 1.4s;

/* Firefox 4 */ 
 -moz-transition-property: width;
 -moz-transition-duration: 1.4s;
/* Safari and Chrome */ 
 -webkit-transition-property: width;
 -webkit-transition-duration: 1.4s;
/* Opera */
  -o-transition-property: background-color, color;  
  -o-transition-duration: 1.4s;

#iddv:hover {

<div id="iddv">Hover over this square.</div>

Demo (When the cursor mouse out of the element, it gradually changes back to its original style):
Hover over this square.

transition shorthand property

You can use all the four components into a single transition shorthand property.
transition: transition-property transition-duration transition-timing-function transition-delay;
Example: Change gradually the "font-size" (in 0.4 seconds, and "ease-out" speed) when the mouse is over an element with class="clse".
<style type="text/css"> 
.clse {
 transition: font-size 0.4s ease-out; 
 -moz-transition: font-size 0.4s ease-out;  /* Firefox 4 */ 
 -webkit-transition: font-size 0.4s ease-out;  /* Safari and Chrome */
  -o-transition: font-size 0.4s ease-out;  /* Opera */

.clse:hover {
 font-size: 16px;

 <li class="clse"><a href="" title="Free CSS Course">Free CSS Course</a></li>
 <li class="clse"><a href="" title="HTML Course">HTML Course</a></li>
 <li class="clse"><a href="" title="Flash Games">Flash Games</a></li>

Demo {place the cursor over each link}:

• You can also add a transitional effect for more than one style, by adding more properties, separated by commas.
Example. Add effects on the background, opacity, and the transformation:
<style type="text/css"> 
.dv1 {

.clsdv {
 transition: background 1.3s, opacity 1.8s, transform 1.4s; 
 -moz-transition: background 1.3s, opacity 1.8s, -moz-transform 1.4s;  /* Firefox 4 */ 
 -webkit-transition: background 1.3s, opacity 1.8s, -webkit-transform 1.4s;  /* Safari and Chrome */
  -o-transition: background 1.3s, opacity 1.8s, -o-transform 1.4s;  /* Opera */

.clsdv:hover {
 background: #00da01;
 filter:alpha(opacity=50);     /* for IE */
 -moz-transform:rotate(180deg); /* Firefox 4 */
 -webkit-transform:rotate(180deg); /* Safari and Chrome */
 -o-transform:rotate(180deg); /* Opera */

Hover over this rectangle.
<div class="dv1">
 <div class="clsdv"></div>
 Some hidden text
Hover over this rectangle.
Some hidden text

CSS animatable properties

List of CSS properties that can be used in transitions (and animations):

- Text properties:   color, font-size, font-weight, letter-spacing, line-height, text-indent, text-shadow, vertical-align, word-spacing.
- Box properties:   background, background-color, background-image, background-position, border-left-color etc., border-spacing, border-left-width etc., clip, crop, height, min-height, max-height, margin-left etc., opacity, outline-width, outline-offset, outline-color, padding-left etc., width, min-width, max-width.
- Positioning properties:   bottom, top, left, right, grid-, visibility, z-index, zoom .

Daily Test with Code Example

Which tag renders as emphasized text, displaying the text oblique?
<strong> <pre> <em>
<p>Web development courses: <em></em></p>
Which CSS property defines the space between the element border and its content?
margin padding position
h3 {
  padding: 2px 0.2em;
Click on the method which returns the first element that matches a specified group of selectors.
getElementsByName() querySelector() querySelectorAll()
// gets first Div with class="cls", and shows its content
var elm = document.querySelector("div.cls");
Indicate the PHP variable that contains data from a form sent with method="post".
if(isset($_POST["field"])) {
  echo $_POST["field"];
CSS3 transition

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