<link rel="icon" 
      type="image/png" 
      href="http://example.com/myicon.png">
ref: https://stackoverflow.com/questions/8988855/include-another-html-file-in-a-html-file
Solution 1. Use jQuery.js
<!doctype html>
<head>
<script src="script/jquery.js"></script> 
<script> $(function(){$("#nav_menu").load("nav_menu.html"); });</script> 
</head>
<body>
<div id="nav_menu"></div>
</div>
</body>
Solution 2. Use a custom javascript
a.html:
<html> 
  <body>
  <h1>Put your HTML content before insertion of b.js.</h1>
      ...
  <script src="b.js"></script>
      ...
  <p>And whatever content you want afterwards.</p>
  </body>
</html>
b.js:
document.write('\
    <h1>Add your HTML code here</h1>\
     <p>Notice however, that you have to escape LF's with a '\', just like\
        demonstrated in this code listing.\
    </p>\
');
Or just use the following handy bash script published as a Gist on Github, that automates all necessary work, converting b.html to b.js: https://gist.github.com/Tafkadasoh/334881e18cbb7fc2a5c033bfa03f6ee6
Solution 3. Use htm file and frameset
<link rel="stylesheet" type="tex/css" href="LSstyle.css">
ln -s /home/wwwroot/LSstyle.css LSstyle.css
#fixWidthBlockRound { border-radius: 4px; }
img.roundedCorner6px{ border-radius:6px; overflow:hidden; }
两者似乎可以互相替换:https://www.w3schools.com/code/tryit.asp?filename=FYJD2ER45BQL
但是class的定义方法必须得指定tag,不如id来得通用[?] 
#navlist {
  position: relative;
}
li.home {
  left: 0px;
  width: 46px;
  background: url('img_navsprites_hover.gif') 0 0;
}
#prev {
  left: 63px;
  width: 43px;
  background: url('img_navsprites_hover.gif') -47px 0;
}
li.home a:hover {
  background: url('img_navsprites_hover.gif') 0 -45px;
}
#prev a:hover {
  background: url('img_navsprites_hover.gif') -47px -45px;
}
<ul id="navlist">
  <li class="home"><a href="default.asp"></a></li>
  <li id="prev"><a href="css_intro.asp"></a></li>
</ul>
参考资料:
 * CSS dropdown menu https://catalin.red/css3-dropdown-menu/