<!-- some codes -->
<meta charset="UTF-8">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<!-- some codes -->
The two lines in the above code are with error.
This document already contains a "meta" element with the "charset" attribute. Documents must not contain both a "meta" element with http-equiv="content-type" and a "meta" element with the "charset" attribute.
The following is a sample code in https://latex.js.org/usage.html#webcomponent
The two lines in the above code are with error.