Change opacity on all elements except hovered one

Question

I wonder if there is a way to lower opacity (on hover) to all of the 'li's' except the one I'm actually hovering? Something similar to this picture:

.main-navigation { 
    margin: 0;
    padding: 20px 0px 25px;
    list-style: none;
    background-color: #ffffff;
    text-align: center;
    display:block;
    font-size:1.1em;    
}
.main-navigation li.hvr a.lvl1:link,
.main-navigation li.hvr a.lvl1:visited 
{
	display: block;
	padding: 5px 2px 5px 3px;
	color: #000;
	text-decoration: none;
    text-align:center;
}
.main-navigation li.hvr a.lvl1.active { 
    background: #eeeeee; 
    color:#000000;
}
.main-navigation li.hvr a.lvl1:hover
{
	background-color: #E6E6E6;
    color:#666666;
} 
.main-navigation li.hvr { 
	float: left; 
	position: relative;
    width:191px;
    margin:0;
    font-family: 'Open Sans', sans-serif;
}
.main-navigation li.hvr:hover { 
	background-color: #E6E6E6;
}
.main-navigation ul { 
	display: none;
	position: absolute;
	top:100%;
	left: 0;
	z-index: 9999;
	background-color: #777;
	margin: 0;
	padding: 0;
	min-width:100%;
	text-align:left;
}
.main-navigation li.hvr:hover ul { display: block; }
.main-navigation li.hvr ul li { 
	margin: 0;
	padding: 0;
	list-style: none;
}
.main-navigation li.hvr ul li a:link,
.main-navigation li.hvr ul li a:visited
{
	display: block;
	padding: 5px 20px;
	color: #fff;
    text-align: center;
}
.main-navigation li.hvr ul li a:hover,
.main-navigation li.hvr ul li a:active
{
    display: block;
    padding: 5px 20px;
    color: #fff;
    background-color:#cccccc;
}

<ul class="main-navigation clearfix">
    <li class="hvr ">
        <a class="lvl1 active" href="">Title 1</a>
        <ul>
            <li><a href="">Sub title 1</a></li>
            <li><a href="">Sub title 2</a></li>
            <li><a href="">Sub title 3</a></li>
        </ul>
    </li>
    <li class="hvr ">
        <a class="lvl1" href="">Title 2</a>
        <ul>
            <li><a href="">Sub title 1</a></li>
            <li><a href="">Sub title 2</a></li>
            <li><a href="">Sub title 3</a></li>
        </ul>
    </li>
    <li class="hvr ">
        <a class="lvl1" href="">Title 3</a>
        <ul>
            <li><a href="">Sub title 1</a></li>
            <li><a href="">Sub title 2</a></li>
            <li><a href="">Sub title 3</a></li>
        </ul>
    </li>
    <li class="hvr ">
        <a class="lvl1" href="">Title 4</a>
        <ul>
            <li><a href="">Sub title 1</a></li>
            <li><a href="">Sub title 2</a></li>
            <li><a href="">Sub title 3</a></li>
        </ul>
    </li>
</ul>

Answer 1

You lower the opacity of all alements except the hovered one with CSS.

The point is to lower the opacity of all <li> elements when the parent (ul) is hovered and to reset the opacity to 1 on the hovered li element like this :

ul:hover li { opacity:0.5; }
ul li:hover { opacity:1; }

Here is a simple demo :

li{
  float:left;
  width:33.33%;
  line-height:50px;
  background:grey;
  list-style-type:none;
}
ul:hover li{
  opacity:0.5;
}
ul li:hover{
  opacity:1;
}

<ul>
  <li>item</li>
  <li>item</li>
  <li>item</li>
</ul>