affect top div opacity without affecting childrne

1#container {
2    border: solid gold 1px;   
3    width: 400px;
4    height: 200px;
5    background:rgba(56,255,255,0.1);
6}
7
8#box {
9    border: solid silver 1px;
10    margin: 10px;
11    width: 300px;
12    height: 100px;
13    background:rgba(205,206,255,0.1);
14  	transition: 2s background;
15}
16
17// if you then want to apply an animation, do it on background-color instead of opacity