設定しました、
#navi ul li:hover { background-color: red; opacity: 1.0; filter: alpha(opacity=100); }
しかし、うまくいきません。
コードは次のとおりです。http://jsfiddle.net/mylvis/jEyTy/
<div id="navi">
<ul>
<li><a href="">1</a></li>
<li><a href="">2</a>
<ul>
<li><a>1.1</a></li>
<li><a>1.2</a></li>
<li><a>1.3</a></li>
</ul>
</li>
<li><a href="">3</a></li>
<li><a href="">4</a></li>
</ul>
</div>
#navi { width: 100%; height: 40px; margin-top: 10px; position: relative; background-color: #0071BC; opacity: 0.75; filter: alpha(opacity=75); font-family: 'Russo One', sans-serif; z-index: 100; }
#navi ul { padding: 0; margin: 0; display: inline-table; text-align: center; position: relative; z-index: 100; }
#navi ul:after { content: ""; clear: both; display: block; }
#navi ul li { display: block; padding: 10px 20px 11px 20px; list-style: none; position: relative; float: left; }
#navi ul li a { font-size: 12pt; color: #F7931E; text-transform: uppercase; }
#navi ul li:hover { background-color: red; opacity: 1.0; filter: alpha(opacity=100); }
#navi ul li:first-child { margin-left: 10px; }
#navi ul li:last-child { margin-left: 210px; }
#navi ul ul { display: none; position: absolute; top: 100%; left: 0; background-color: #0071BC; opacity:0.75; filter:alpha(opacity=75); z-index: 100; }
#navi ul ul li { float: none; position: relative; font-size: 11pt; }
#navi ul ul li:first-child { margin: 0; }
#navi ul ul li:last-child { padding-bottom: 10px; margin: 0; }
#navi ul li:hover > ul { display: block; z-index: 100; }