css伪类选择器为什么不工作：focus div

Question

When the mouse hover on the menus,the menu items can show up,but I want to use "Tab" key to focus on the menu and the menu items can show up,but it doesn't work,how can I fix it?

Here's HTML

<ul class="hMenu">
        <li><a href="">prod1</a>
            <div>
                <a href="">test1</a>
                <a href="">test2</a>
                <a href="">test3</a>                    
            </div>
        </li>
        <li><a href="javascript:void(0);" >prod2</a>
            <div>                                               
                <a href="">test4</a>    
                <a href="">test5</a>                    
            </div>
        </li>    
    </ul>   

Here's css:

ul.hMenu li:hover a { color:red;}           
        ul.hMenu li div table{  background-color:yellow;}    
        ul.hMenu  { 
            margin: 0;
            padding: 0; 
            z-index: 1;                 
        }
        ul.hMenu li  {  
            margin: 0;
            padding: 0;
            list-style: none;
            float: left;
            width:140px;
        }
        ul.hMenu li a { 
            display: block; 
            text-align: left;
            text-decoration: none
        }          
        ul.hMenu li div  {                    
            position: absolute;             
            display: none;                
        }
        ul.hMenu div a {background: yellow;     
        }
        ul.hMenu li :hover   {  background: yellow}
        /**Mouse hover the menus can show up**/
        ul.hMenu li:hover   div{            
            display:block;
        }
        /**Why this line can not work when the "Tab" to focus on the menu？**/
        ul.hMenu li :focus  div{            
            display:block;
        }

Answer 1

If you have copied the code directly, what I see is that you have a space between your li and focus. Please remove the spaces between :hover or :focus and the previous element and try again.

Adding a space means you are referring to a descendant element which is not the case.

Answer 2

Try this,

ul.hMenu li:focus  div{            
    display:block;
}

And

ul.hMenu li:hover   {  background: yellow}

Answer 3

This should do it:

ul.hMenu li a:focus + div{            
        display:block;
    }    

Example: Demo

And play around a bit with

 tabindex="myNumber"

in the appropriate html elements :)