WebSteve, do you understand the problem?
To target a different set of list items, you need to override the styles assigned by materializecss CSS and possibly other styles that may be imposed by other plug-ins that we are as yet unaware of.
Specificity is the key to overrides. Look it up and study it if you don't know what specificity means. Overrides are usually (but not always) accomplished by adding classes to the new
<ul> and possibly the new
<li> list items. However, it is done, the overrides must either be the same "weight" (specificity) as those being overridden and must be placed later in your CSS than those being overridden OR the overrides must have greater specificity ("weight") than those being overridden.
Without access to the complete code affecting the site, all we can do is guess. So far, it appears that you do not know enough about HTML and CSS to understand simple overrides. It's essential that you know how to use the browser's dev tools to read the HTML and CSS.
Create a test page. Study the concept of specificity. Experiment with it. Apply it to your site. You will have learned something and fixed your problem all by yourself.
Otherwise, give us a link to your test site so we can see the all of the code instead of just an isolated peek. As a rule of thumb, HTML and CSS does not work in isolation to its surroundings. It's a whole package.