How do I inline the :before element when unable to include a CSS/style section?

You can insert a new stylesheet inline with the following HTML:

<style>
  li:before { color: red; }
</style>

The reason this is the only way to do it is that :before is a pseudo-element, meaning that it doesn't actually become part of the DOM. Unfortunately, this means there is no way to style it inline, as requested.

As an example:

<li style="color: red;">text</li>

would style the entire LI element, not just it's :before pseudo-element, and because the :before element has no markup, it can not have it's own style= property.

In CSS, inline styles take precedence over linked CSS files, so you could do something like this with your li elements:-

<li style="color: red;">This is a list item</li>

And it would take precedence over either a linked stylesheet, or an internal stylesheet.

If you're wanting to use more complex selectors, you're out of luck unfortunately.

See: CSS Pseudo-classes with inline styles