Infinite Multilevel Dropdown

index.html

<ul class="nav site-nav">
    <li><a href=#>Lorem</a></li><!--
 --><li><a href=#>Ipsum</a></li><!--
 --><li class=flyout>
    
        <a href=#>Dolor</a>
        
        <!-- Flyout -->
        <ul class="flyout-content nav stacked">
            <li><a href=#>Foo Bar</a></li>
            <li><a href=#>Bar Baz</a></li>
            <li class="flyout-alt">
                
                <a href=#>Baz Foo</a>
                
                <!-- Flyout -->
                <ul class="flyout-content nav stacked">
                    <li><a href=#>Foo Bar</a></li>
                    <li><a href=#>Bar Baz</a></li>
                    <li class="flyout-alt">
                        
                        <a href=#>Baz Foo</a>
                        
                        <!-- Flyout -->
                        <ul class="flyout-content nav stacked">
                            <li class="flyout-alt">
                                
                                <a href=#>Foo Bar</a>
                                
                                <!-- Flyout -->
                                <ul class="flyout-content nav stacked">
                                    <li><a href=#>Bar Baz</a></li>
                                    <li class="flyout-alt">
                                        
                                        <a href=#>Baz Foo</a>
                                        
                                        <!-- Flyout -->
                                        <ul class="flyout-content nav stacked">
                                            <li><a href=#>Bar Baz</a></li>
                                            <li><a href=#>Baz Foo</a></li>
                                            <li><a href=#>Foo Bar</a></li>
                                        </ul>
                                    
                                    </li>
                                    <li><a href=#>Foo Bar</a></li>
                                </ul>
                                
                            </li>
                            <li><a href=#>Bar Baz</a></li>
                            <li class="flyout-alt">
                                
                                <a href=#>Baz Foo</a>
                                
                                <!-- Flyout -->
                                <ul class="flyout-content nav stacked">
                                    <li><a href=#>Bar Baz</a></li>
                                    <li><a href=#>Baz Foo</a></li>
                                    <li><a href=#>Foo Bar</a></li>
                                </ul>
                                
                            </li>
                        </ul>
                        
                    </li>
                </ul>
                
            </li>
        </ul>
    
    </li><!--
 --><li><a href=#>Sit</a></li><!--
 --><li><a href=#>Amet</a></li>
</ul>​

infinite-multilevel-dropdown.markdown

Infinite Multilevel Dropdown

Infinite dropdown menu courtesy of Harry Roberts ‏@csswizardry http://jsfiddle.net/csswizardry/Zj4eb/

A Pen by design8383 on CodePen.

License.

style.css

/*------------------------------------*\
    $HOUSEKEEPING
\*------------------------------------*/
*{ margin:0; padding:0; }
html{
    padding:5%;
    font:1em/1.5 Georgia, serif;
    overflow-y:scroll;
}
ul{
    margin-bottom:1.5em;
    margin-left:1.5em;
}
a{
    text-decoration:none;
}





/*------------------------------------*\
    $NAV
\*------------------------------------*/
/**
 * Throw any `ul` or `ol` into horizontal mode, as per csswizardry.com/2011/09/the-nav-abstraction.
   <ul class=nav>
       <li><a href=/>Home</a></li>
       <li><a href=/about>About</a></li>
       <li><a href=/portfolio>Portfolio</a></li>
       <li><a href=/contact>Contact</a></li>
   </ul>
 */
.nav{
    list-style:none;
    margin-left:0;
}
    .nav > li,
        .nav > li > a{
            display:inline-block;
           *display:inline;
            zoom:1;
        }
    
    /**
     * Create a vertically stacked nav by extending `.nav` with `.stacked`.
       <ul class="nav stacked">
           <li><a href=/>Home</a></li>
           <li><a href=/about>About</a></li>
           <li><a href=/portfolio>Portfolio</a></li>
           <li><a href=/contact>Contact</a></li>
       </ul>
     */
    .stacked > li{
        display:list-item;
    }
        .stacked > li > a{
            display:block;
    }





/*------------------------------------*\
    $FLYOUT
\*------------------------------------*/
/**
 * Flyouts are pieces of content that fly out of a parent when said parent is hovered.
 * They typically appear bottom-left of the parent.
   <div class=flyout>
       Foo
       <div class=flyout-content>
           <h1>Lorem</h1>
           <p>Ipsum</p>
       </div>
   </div>
 */
.flyout,
.flyout-alt{
    position:relative;
}
    .flyout-content{
        /* Position the flyouts off-screen. This is typically better than `display:none;`. */
        position:absolute;
        top:100%;
        left:-99999px;
        /**
         * Even though they are out of document flow, lots of nested flyouts can
         * eventually force scroll bars to appear as they become taller than the viewport.
         * We can undo this effect by giving them zero height.
         */
        height:0;
        overflow:hidden;
    }
    
    /**
     * Bring the flyouts into view when you hover their parents.
     * Two different types of flyout; ‘regular’ (`.flyout`) and ‘alternative’ (`.flyout-alt`).
     */
    /* Regular flyouts sit all the way from the top, flush left. */
    .flyout:hover > .flyout-content{
        left:0;
    }
    /* Alternative flyouts sit all the way from the left, flush top. */
    .flyout-alt:hover > .flyout-content{
        top:0;
        left:100%;
    }
    .flyout:hover > .flyout-content,
    .flyout-alt:hover > .flyout-content{
        /* Give the flyouts their height back once they come into view. */
        height:auto;
        overflow:visible;
    }





/*------------------------------------*\
    $SITE-NAV
\*------------------------------------*/
/**
 * Site nav specific styling.
 * Extends `.nav{}`
 */
.site-nav{
    font-size:0.75em;
    font-family:sans-serif;
}
        .site-nav a{
            line-height:1;
            padding:1em;
            background-color:#09f;
            color:#fff;
            white-space:nowrap;
        }

/*--- SITE-NAV FLYOUTS ---*/
/**
 * Site nav specific flyouts, extension of `.flyout`.
 * Set up some styles to apply and persist when we hover things in the site nav.
 * This allows us to keep parents highlighted as we hover their contained flyouts [1].
 */
.site-nav .flyout:hover > a /* [1] */,
.site-nav .flyout-alt:hover > a /* [1] */,
.site-nav a:hover{
    color:#435704;
    background-color:#BADA55;
}

/**
 * Add an indicator to any flyout parents in the site nav to show there’s a flyout.
 */
.site-nav .flyout-alt > a:after{
    content:" »";
}

/**
 * Here we set up a load of shared borders on the site-nav specific flyouts.
 * The code looks a little scattered but it allows us to cleverly share declarations:
 * We set up a non-existent [1] solid [2] border on all sides of the relevant elements.
 * We can now also change the style [2] and colour [3] of all borders in one go.
 * Now we have set up border colours and styles, we need to just turn the desired borders ‘on’ [4].
 */
.site-nav a,
.site-nav .flyout-content{
    border:0     /* [1] */
           solid /* [2] */
           #fff  /* [3] */;
}
.site-nav > li > a{
    border-left-width:1px; /* [4] */
}
/* The first link in the site-nav doesn’t require a border at all. */
.site-nav > li:first-child > a{
    border:none;    
}
.site-nav .flyout-content{
    border-width:1px 0 0 1px; /* [4] */
}
.site-nav .flyout-content a{
    border-bottom-width:1px; /* [4] */
}
.site-nav .flyout-alt:hover > .flyout-content{
    /**
     * To account for the 1px top border on the flyout containers, we need to
     * bring the flyouts back up by 1px in this special instance.
     */
    top:-1px;
}​