Thanks @davy-landmann for https://stackoverflow.com/a/638064/417153.
That's what I was looking for! Same effect with LESS code:
@searchResultMinHeight = 200px;
.searchResult {
min-height: @searchResultMinHeight;
position: relative;
.innerTrans {
background: white;
.opacity(0.5);
min-height: @searchResultMinHeight;
}
.innerBody {
padding: 0.5em;
position: absolute;
top: 0;
}
}