Changing background image when hovering on a list item

Question

As you can see in the screenshot, I've got an unordered list. Now the div of this list has a background image. What I want to do is to change background's image whenever I hover the mouse on a list item. Note that every item should change background to a different image. How do I do this? I've only found answers how to change to a single, not multiple images.

Here's the screenshot.

I've already hovered on the first item of the list.

div's CSS:

.body {
  display: block;
  float: left;
  background-image: url("bgdef.jpg");
  background-repeat: no-repeat;
  position: static;
  width: 100%;
  height: auto;
  margin: 0;
}

.menu {
  width: 250px;
  padding: 0;
  margin: 100px 0px 33% 75%;
  list-style-type: none;
  -webkit-touch-callout: none;
  -webkit-user-select: none;
  -khtml-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
  -webkit-user-drag: none;
}

.menu a:link,
a:visited,
a:hover,
a:active {
  text-decoration: none;
  bottom: auto;
  padding-bottom: auto;
  text-shadow: none;
}

.menu li {
  background-color: white;
  margin: 10px;
  padding: 3px 0 3px 10%;
  border-radius: 10PX 0 0 10px;
  font-size: 20px;
}

.menu li:hover {
  background-color: green;
  margin-right: 18px;
  margin-left: 1px;
}

Answer 1

You can do this by CSS only. It's a trick and in the most of the cases you will need to use JS, but its working and working good! (See it in Full Page)

.wrapper {
  width:900px;
  height:600px;
  position:relative;
}

.item {
  position:relative;
  z-index:1;
}

.bg {
  position:absolute;
  top:0;
  left:0;
      width: 100%;
    height: 100%;
}

.bg img {
  position:absolute;
  top:0;
  left:0;
  width:100%;
  height:100%;
  opacity:0;
  transition:all .3s ease;
}

.bg img:nth-child(1),
.item:nth-child(1):hover ~ .bg img:nth-child(1),
.item:nth-child(2):hover ~ .bg img:nth-child(2),
.item:nth-child(3):hover ~ .bg img:nth-child(3) {
  opacity:1;
}

<div class="wrapper">
    <div class="item">Item 1</div>
    <div class="item">Item 2</div>
    <div class="item">Item 3</div>
    <div class="bg">
      <img src="http://i.stack.imgur.com/tq1uR.jpg" />
      <img src="http://i.stack.imgur.com/ZAy9V.jpg" />
      <img src="http://i.stack.imgur.com/xfvXS.jpg" />
    </div>
  </div>

Answer 2

Since there is still no CSS parent selector you can use jQuery

#container {
    width: 800px;
    height: 600px;
    background: url(http://filepic.ru/file/1441522670.jpg);
}
#container li {
    display: block;
    margin: 5px;
    float: right;
    clear: both;
    background-color: #fff;
    width: 150px;
}
#container li:hover {
    background-color: green;
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<div id="container">
  <ul>
    <li onmouseover="$('#container').css('background','url(http://filepic.ru/file/1441522623.jpg)');">1</li>
    <li onmouseover="$('#container').css('background','url(http://filepic.ru/file/1441522645.jpg)');">2</li>
    <li onmouseover="$('#container').css('background','url(http://filepic.ru/file/1441522653.jpg)');">3</li>
    <li onmouseover="$('#container').css('background','url(http://filepic.ru/file/1441522662.png)');">4</li>
    <li onmouseover="$('#container').css('background','url(http://filepic.ru/file/1441522670.jpg)');">5</li>
  </ul>
</div>