要素をトリガーして、ホバー時に非表示の要素を表示したい
HTML
<div class="contents">
<aside>
<section class="tumb">
<a class="placeHoldTumb" href="#"><img src="http://placehold.it/100x100">
<a class="placeHoldTumb" href="#"><img src="http://placehold.it/100x100">
</section>
</aside>
<div class="hidden">
<a href="#" class="one" ><img src="http://placehold.it/1000x1000/bada55" width="500px" ></a>
<a href="#" class="two" ><img src="http://placehold.it/1000x1000/bada55" width="500px" ></a>
</div>
<a href="#" class="background" ><img src="http://placehold.it/1000x1000/000000/bada55" width="500px" /></a>
</div><!-- end contents -->
CSS
aside {
z-index: 100;
background: rgba(0, 182, 173, 0.9);
width: 230px;
position: absolute; }
aside .tumb img {
margin: 5px; position: relative; }
.contents img {
position: absolute; }
.hidden img { opacity: 0; }
.tumb a:hover ~ .hidden img {
opacity: 1;
filter:alpha(opacity=100); /*For IE8*/ }