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The <time> CSS data type specifies a duration in time, expressed as a number followed (without whitespace) by one of the time unit abbreviations: s or ms.

In CSS3, time units must be either seconds (s) or milliseconds (ms); milliseconds are one-thousandth of a second. Time values can be used to measure the duration of animation effects, in which case the numeric value must be greater than or equal to zero.


.changeable {
    background-color: #fff;
    transition-property: background-color;
    /* transition takes half a second to complete */
    transition-duration: 0.5s;
.changeable:hover {
    background-color: #ff4;
    /* transition to yellow on mouseover */

Related specifications

CSS Values and Units Module Level 3
Candidate Recommendation