change other element when mouse over in CSS

Question

i want to change other element outside current element level in CSS3. i have tried to use plus symbol but still not working.

    <div id="a">
<div id="a_1">
<ul>

<li>test1</li>
<li>test2</li>
</ul>
</div>
</div>

<div id="b">
</div>

i want to change #b background-color i try this but not still work

a ul li:hover #b{
background-color:blue;
}

and also tried this but not working too

a ul li:hover + #b{
background-color:blue;
}

Answer 1

You must use JavaScript or JQuery for that.