Css Study - 纵向Menu - By html and Css

<div id="leftmenu">
            <ul>
                <li><a href="#">Home</a></li>
                <li class=‘has-sub‘><a href="#">PRODUCTS</a>
                    <ul>
                        <li class=‘has-sub‘><a href="#">Sub Product1</a>
                            <ul>
                                <li class=‘no-sub‘><a href="#">Sub Product1-1</a>
                                </li>
                                <li class=‘no-sub‘><a href="#">Sub Product1-2</a></li>
                            </ul>
                        </li>
                        <li class=‘no-sub‘><a href="#">Sub Product2</a></li>
                    </ul>
                </li>
            </ul>
        </div>

<style>
        /* Starter CSS for Flyout Menu */
        #leftmenu {
            padding: 0;
            margin: 0;
            border: 0;
        }

            #leftmenu ul,
            li {
                list-style: none;
                margin: 0;
                padding: 0;
            }

            #leftmenu ul {
                position: relative;
                z-index: 597;
                float: left;
            }

                #leftmenu ul li {
                    float: left;
                    height: 38px;
                    line-height: 38px;
                    width: 200px;
                    vertical-align: middle;
                }

                    #leftmenu ul li.hover,
                    #leftmenu ul li:hover {
                        position: relative;
                        z-index: 599;
                        cursor: default;
                    }

                #leftmenu ul ul {
                    visibility: hidden;
                    position: absolute;
                    top: 100%;
                    left: 0;
                    z-index: 598;
                    width: 100%;
                }

                    #leftmenu ul ul li {
                        float: none;
                    }

                #leftmenu ul li:hover > ul {
                    visibility: visible;
                }

                #leftmenu ul ul {
                    top: 0;
                    left: 100%;
                }

                #leftmenu ul li {
                    float: none;
                }
        /* Custom Stuff */
        #leftmenu {
            border-radius: 5px;
            background-clip: padding-box;
            box-shadow: 0 0 2px 1px rgba(0, 0, 0, 0.15);
            width: 160px;
        }

            #leftmenu span,
            #leftmenu a {
                display: inline-block;
                font-family: Arial, Helvetica, sans-serif;
                font-size: 12px;
                text-decoration: none;
                border-bottom: solid 1px rgba(0, 0, 0, 0.15);
            }

            #leftmenu:after,
            #leftmenu ul:after {
                content: ‘‘;
                display: block;
                clear: both;
            }

            #leftmenu > ul > li ul ul {
                border-radius: 0 6px 6px 0;
                background-clip: padding-box;
                background-color: #ffffff;
            }

            #leftmenu ul,
            #leftmenu li {
                background-color: #4cb6ea;
                font-weight: bold;
                width: 100%;
            }

            #leftmenu li {
                height: 25px;
                line-height: 25px;
            }

            #leftmenu a {
                color: #ffffff;
                line-height: 160%;
                padding: 8px 20px 8px 20px;
                width: 120px;
                font-size: 16px;
            }

                #leftmenu a:hover {
                    color: #666;
                    background: #ffffff;
                }

            #leftmenu ul ul {
                width: 160px;
                border: 1px solid #dddddd;
                background: #ffffff;
            }

                #leftmenu ul ul li {
                    background: #ffffff;
                }

                    #leftmenu ul ul li a {
                        color: #666;
                    }

                        #leftmenu ul ul li a:hover {
                            color: #ff006e;
                        }

            #leftmenu .has-sub {
                position: relative;
            }

            #leftmenu ul .has-sub a:before {
                display: block;
                content: "";
                border: 6px solid transparent;
                border-left-color: #eee;
                z-index: 2;
                height: 0;
                width: 0;
                position: absolute;
                right: 12px;
                top: -2px;
            }

            #leftmenu .has-sub:hover a:before {
                border-left-color: #666;
            }

            #leftmenu .has-sub:hover ul li a:before {
                display: none;
            }

            #leftmenu .has-sub:hover .has-sub a:before {
                display: block;
            }

            #leftmenu .has-sub:hover .has-sub:hover a:before {
                border-left-color: #ff006e;
            }

            #leftmenu .has-sub:hover .has-sub:hover ul li a:before,
            #leftmenu .no-sub a:before,
            #leftmenu .no-sub:hover a:before {
                display: none;
            }
    </style>