https://katex.org/docs/browser.html

Loading as Global:
{{{#!html
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/katex@0.16.7/dist/katex.css" integrity="sha384-YiVwk+MBV52+yIvvplLwDxm3iGDI7dYb731lqsN9ASGBpIpJ/dte35lBIuR5oGFU" crossorigin="anonymous">
<script defer src="https://cdn.jsdelivr.net/npm/katex@0.16.7/dist/katex.js" integrity="sha384-8JJEhHkwY0VI06p7huKe7LqvYgDhSS69qJxWSQGwlB8FmDnAgPKgZGk5Ui0VyuNH" crossorigin="anonymous"></script>
}}}

----
https://katex.org/docs/api.html
In-browser rendering
1.
[[HTML(<script>katex.render("c = \\pm\\sqrt{a^2 + b^2}", element, {    throwOnError: false});</script>)]]

2.
{{{#!html
<script>
katex.render(String.raw`c = \pm\sqrt{a^2 + b^2}`, element, {
    throwOnError: false
});
</script>
}}}