Check out example codes for "effetto fade con css". It will help you in understanding the concepts better.

Code Example 1

.fade {
opacity: 1;
transition: opacity .25s ease-in-out;
-moz-transition: opacity .25s ease-in-out;
-webkit-transition: opacity .25s ease-in-out;
}
 
.fade:hover {
opacity: 0.5;
}

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