html, body {
    margin: 0;
    padding: 0;
}
body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    color: #333;
}
header {
    background-color: darkslategray;
    height: 52px;
    color: white;
    line-height: 52px;
    font-size: 20px;
    padding-left: 16px;
}

footer {
    background-color: darkslategray;
    height: 60px;
    line-height: 30px;
    color: white;
    text-align: center;
    position: fixed;
    bottom: 0;
    width: 100%;
}
footer > span {
    margin-right: 40px;
}
footer > a {
    color: white;
    text-decoration: none;
}

#beian_no {
    color: white;
    text-decoration: none;
}
#beian_no:hover {
    color: #337ab7;
}

main {
    width: 60%;
    margin: 0 auto;
    margin-bottom: 50px;
}

main a {
    color: #337ab7;
    text-decoration: none;
    margin-right: 6px;
}

main a:hover, main a:focus {
    color: #23527c;
    text-decoration: underline;
}

main a:hover, main a:active {
    outline: 0;
}

.container {
    display: flex;
}

.container .col {
    margin-right: 40px;
}

/* 参考达内的链接 */
.doc-refs {
    margin: 20px;
}