How transition property works?

Answer 1

CSS3 transitions allows you to change property values smoothly (from one value to another), over a given duration.
To create a transition effect, you must specify two things:
the CSS property you want to add an effect to
the duration of the effect
Note: If the duration part is not specified, the transition will have no effect, because the default value is 0.
Source: https://www.w3schools.com/css/css3_transitions.asp
More info: https://www.w3schools.com/css/css3_transitions.asp

Answer 2

thank you.. gonna check your links so i can understand it more