CSS lighten child elements on parent mouseover

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Live Demo

Relevant CSS:

#container:hover .inner {
    opacity: 0.8
}

HTML:

<div id="container">
    <div id="left" class="inner"></div>
    <div id="right" class="inner"></div>
</div>

Irrelevant CSS:

#container {
    width: 300px;
    padding: 30px;
    overflow: hidden
}

.inner {
    width: 40%;
    height: 250px;
    background: #ccc
}
#left {
    float: left
}
#right {
    float: right
}

Truly Irrelevant CSS:

#container {
    background: #fcecfc; /* old browsers */
    background: -moz-linear-gradient(top, #fcecfc 0%, #fba6e1 50%, #fd89d7 51%, #ff7cd8 100%); /* firefox */

    background: -webkit-gradient(linear, left top, left bottom, color-stop(0%,#fcecfc), color-stop(50%,#fba6e1), color-stop(51%,#fd89d7), color-stop(100%,#ff7cd8)); /* webkit */

    filter: progid:DXImageTransform.Microsoft.gradient( startColorstr="#fcecfc", endColorstr="#ff7cd8",GradientType=0 ); /* ie */
}