Hover to Reveal Hidden Element

HTML

<div class="outer">

        
    </div>  
<div class="right">
    <div class="inner">
    </div>
    
</div>

CSS

div.outer:hover div.inner {
    background: red;
    display: block;
}

div.outer {
    width: 100px;
    height: 100px; 
    padding: 2px;
    border: thin dashed black;
}

div.inner {
    width: 100px;
    height: 100px; 
    display: none;
}