body {

}

header {
    background-color: black;
    color: white;
    text-align: center;
    padding: 5px;
    clear: right; /*Òònav float£¬·ÀÖ¹Öصþ*/
    font-size:50px;
}

nav {
    background-color: grey;
    width: 100%;
    height: 70px;
    font-size: 28px;
    font-weight: bold;
    color: black;
}

nav a {
    text-decoration: none;
    color: black;
}

nav > ul {
    list-style-type: none;
    margin: 0px;
    padding: 0px;
}

nav li:link, nav li:visited {
    background-color: grey;
}

nav li:hover, nav li:active {
    background-color: #cc0000;
}

nav ul.drop-menu:hover {
    background-color: white;
}

nav ul.drop-menu:hover li.second-menu {
    display: block;
    font-size: smaller;
}

nav li.second-menu {
    display: none;
}

nav > ul > li {
    float:left;
    text-align: center;
    margin: 10px;
    padding: 0px;
}

nav > ul > li > ul {
    list-style-type: none;
    margin: 0px;
    padding: 0px;
}

article {
    padding: 10px;
    clear: left; /*Òònav float£¬·ÀÖ¹Öصþ*/
}

footer {
    background-color: black;
    color: white;
    text-align: center;
    padding: 5px;
}