.a:hover .a-box {
background-color: none;
opacity: 1;
filter: none;
}
.a-box {
opacity: 0.3;
filter: alpha(opacity=30);
background-color: #000;
background-color: rgba(37, 36, 36, 0.6);
}
<html>
<div class="a">
<div class="a-box"></div>
</div>
</html>
