Hover/reveal CSS help

Hi,

I’m using this bit of css to control a :hover over an image to reveal a set of text & images below.

#lp-pom-image-232 {
    opacity: 0.0;
    -webkit-transition: all 500ms ease-in-out;
    -moz-transition: all 500ms ease-in-out;
    -ms-transition: all 500ms ease-in-out;
    -o-transition: all 500ms ease-in-out;
    transition: all 500ms ease-in-out;
}
#lp-pom-image-223:hover + #lp-pom-image-232 {
    opacity: 1.0;
}

It isnt working in preview mode and i can’t work out why.