CSS

low opacity whit out toching child nods

#container {
    opacity: 0.3;
    background-color: #777788;
    position: absolute;
    top: 100px;
    left: 100px;
    height: 150px;
    width: 300px;
}
#box {
    opacity: 1;
    background-color: #ffffff;
    position: absolute;
    top: 110px;
    left: 110px;
    height: 130px;
    width: 270px;
}
<div id="container"></div>
<div id="box">
    <p>Something in here</p>
</div>