我看了一些其他答案,如here和here,但我无法弄明白.

这是一段视频,解释了我想要完成的任务：http://screencast.com/t/Bhfj6mtZkPZp

这是导航代码：

.primary-navigation {
    max-width: 1192px;
    margin: 20px 0px 52px 1px;
}
 
.primary-navigation ul {
    font-family: 'Josefin Sans',sans-serif;
    font-size: 18px;
    font-size: 1.125rem;
    font-weight: bold;
    margin: 0;
    padding: 0;
    list-style: none;
}
 
.primary-navigation ul li {
    display: block;
    position: relative;
    float: left;
}
 
.primary-navigation li ul {
    display: none;
}
 
.primary-navigation ul li a {
    display: block;
    text-decoration: none;
    color: #fff;
    background: #ec6397;
    padding: 12px 22px 17px 22px;
    white-space: nowrap;
    -moz-transition: all 0.25s ease-in-out;
    -webkit-transition: all 0.25s ease-in-out;
    transition: all 0.25s ease-in-out;
    border-right: 1px solid #f39cbd;
}
 
.primary-navigation ul li a:hover { 
    background: #f39cbd;
}
 
.primary-navigation li:hover ul {
    display: block;
    position: absolute;
    border-top: 1px solid #f39cbd;
    border-left: 1px solid #f39cbd;
}
 
.primary-navigation li:hover li {
    float: none;
    width: 300px;
    z-index: 3;
    border-bottom: 1px solid #f39cbd;
}
 
.primary-navigation li:hover a {
    background: #ec6397;
}
 
.primary-navigation li:hover li a:hover {
    background: #f39cbd;
    color: #000;
}