влиять на топ -непрозрачность, не затрагивая ребенка
#container {
border: solid gold 1px;
width: 400px;
height: 200px;
background:rgba(56,255,255,0.1);
}
#box {
border: solid silver 1px;
margin: 10px;
width: 300px;
height: 100px;
background:rgba(205,206,255,0.1);
transition: 2s background;
}
// if you then want to apply an animation, do it on background-color instead of opacity
Enthusiastic Earthworm