Custom HTML in page with ALB / CSS issue

I’ve added a Text Block using the ALB and used the “Text” tab to add some custom HTML. This HTML is similar to:

<div class="my_class">example text</div>

I’m currently using a Child Theme that I created for Enfold, which only has the stylesheet style.css. Adding in the CSS to add the property display: none !important; does not work. The text, in my example listed above, renders properly on the page as “example text”.

I’ve also attempted to “get the CSS to apply” by adding it to /enfold/css/custom.css, and within the Theme Options’ Custom CSS area. None of these resolve my issue.

How do I go about adding in custom CSS in this manner? Keep in mind that an inline solution will not work for me, as the actual code includes media queries and is a fair bit more complex than what I have shown here.