如何在点击时更改菜单的样式？

How can I change the style of active menu/submenu which is selected by user? When I click a submenu, I want that submenu and its parent menu to have a different style (like hover, but permanent).

/*jQuery time*/
$(document).ready(function(){
    $("#accordian h3").click(function(){
        //slide up all the link lists
        $("#accordian ul ul").slideUp();
        //slide down the link list below the h3 clicked - only if its closed
        if(!$(this).next().is(":visible"))
        {
            $(this).next().slideDown();
        }
    })
})

/*custom font for text*/
@import url(http://fonts.googleapis.com/css?family=Nunito);
/*CSS file for fontawesome - an iconfont we will be using. This CSS file imported contains the font-face declaration. More info: http://fortawesome.github.io/Font-Awesome/ */
@import url(http://thecodeplayer.com/uploads/fonts/fontawesome/css/font-awesome.min.css);

/*Basic reset*/
* {margin: 0; padding: 0;}

body {
    background: #4EB889;
    font-family: Nunito, arial, verdana;
}
#accordian {
    background: #004050;
    width: 250px;
    margin: 100px auto 0 auto;
    color: white;
    /*Some cool shadow and glow effect*/
    box-shadow: 
        0 5px 15px 1px rgba(0, 0, 0, 0.6), 
        0 0 200px 1px rgba(255, 255, 255, 0.5);
}
/*heading styles*/
#accordian h3 {
    font-size: 12px;
    line-height: 34px;
    padding: 0 10px;
    cursor: pointer;
    /*fallback for browsers not supporting gradients*/
    background: #003040; 
    background: linear-gradient(#003040, #002535);
}
/*heading hover effect*/
#accordian h3:hover {
    text-shadow: 0 0 1px rgba(255, 255, 255, 0.7);
}
/*iconfont styles*/
#accordian h3 span {
    font-size: 16px;
    margin-right: 10px;
}
/*list items*/
#accordian li {
    list-style-type: none;
}
/*links*/
#accordian ul ul li a {
    color: white;
    text-decoration: none;
    font-size: 11px;
    line-height: 27px;
    display: block;
    padding: 0 15px;
    /*transition for smooth hover animation*/
    transition: all 0.15s;
}
/*hover effect on links*/
#accordian ul ul li a:hover {
    background: #003545;
    border-left: 5px solid lightgreen;
}
/*Lets hide the non active LIs by default*/
#accordian ul ul {
    display: none;
}
#accordian li.active ul {
    display: block;
}

<script src="http://thecodeplayer.com/uploads/js/jquery-1.7.1.min.js"></script>
<script src="http://thecodeplayer.com/uploads/js/prefixfree-1.0.7.js"></script>
<div id="accordian">
    <ul>
        <li>
            <h3><span class="icon-dashboard"></span>Dashboard</h3>
            <ul>
                <li><a href="#">Reports</a></li>
                <li><a href="#">Search</a></li>
                <li><a href="#">Graphs</a></li>
                <li><a href="#">Settings</a></li>
            </ul>
        </li>
        <!-- we will keep this LI open by default -->
        <li class="active">
            <h3><span class="icon-tasks"></span>Tasks</h3>
            <ul>
                <li><a href="#">Today's tasks</a></li>
                <li><a href="#">Urgent</a></li>
                <li><a href="#">Overdues</a></li>
                <li><a href="#">Recurring</a></li>
                <li><a href="#">Settings</a></li>
            </ul>
        </li>
        <li>
            <h3><span class="icon-calendar"></span>Calendar</h3>
            <ul>
                <li><a href="#">Current Month</a></li>
                <li><a href="#">Current Week</a></li>
                <li><a href="#">Previous Month</a></li>
                <li><a href="#">Previous Week</a></li>
                <li><a href="#">Next Month</a></li>
                <li><a href="#">Next Week</a></li>
                <li><a href="#">Team Calendar</a></li>
                <li><a href="#">Private Calendar</a></li>
                <li><a href="#">Settings</a></li>
            </ul>
        </li>
        <li>
            <h3><span class="icon-heart"></span>Favourites</h3>
            <ul>
                <li><a href="#">Global favs</a></li>
                <li><a href="#">My favs</a></li>
                <li><a href="#">Team favs</a></li>
                <li><a href="#">Settings</a></li>
            </ul>
        </li>
    </ul>
</div>

Here is a JSFiddle.

</div>

Just add this javascript code:

$("#accordian h3").click(function(){
      $('.active').removeClass('active');
      $(this).addClass('active');
});
$('#accordian li a').click(function(){
     $('.submenu-active').removeClass('submenu-active');
     $(this).addClass('submenu-active');
});

and this CSS:

.active{
    text-shadow: 0 0 1px rgba(255, 255, 255, 0.7);
    color: red; /* NOTE i INTENTIONALLY ADDED RED COLOR TO ILLUSTRATE BETTER */
}
.submenu-active{
    background: #003545;
    border-left: 5px solid lightgreen;
}

try this DEMO

Explanation:

When you click on a menu item you want to remove the .active class from the previously active item and set it to the clicked item. The same is applied to the submenu item where I add .submenu-active class instead .active

You can add .selected class to your CSS file:

.selected {
    background-color: <your_color>;
}

And in your Javascript file:

$('#accordian li  ul  li').click(function(){
    $('#accordian li  ul  li').removeClass('selected');
    $(this).addClass('selected');
});

Create a css class with style you want. Add some class to your li's (for example class="li_to_click". Then use following code:

$('.li_to_click').click(function() {
    $(this).toggleClass('class_with_style');
    $(this).parent().toggleClass('class_with_style');
});

You may want to change the code according to your needs.