On the product pages of my website I can't style the drop-down for product attributes. The label and the value are there, but I changed the background of my website to black, so now the dropdown box is black on a black background: 
You can see the dropdown when you click on it, but it's not clear it's there on the page otherwise: 
I've had trouble reaching this part of the page template because it's in a deeper grouping of components called 'Add To Cart With Options'. So I can't edit the individual components in that section, nor can I find all of them to recreate the content on the page.
I've added CSS to make the background of Values white in my theme, and every block in the template housing that group of blocks, but it's still not changing.
Something somewhere is overriding the styles I've set up because my 'Add to cart' button in the same group should be white with black text, but it is black with white text like the default style. The button styles correctly in the template preview, but not on a live page. And the Size value does not preview at all on the template so I can't use that view for testing.
Is there anything else I should look at to change this? It's driving me nuts at the moment because it's limiting what I can list on my website if attribute options aren't clear.
value { background-color: #ffffff }which worked when I put it in the label class through inspect element. As mentioned, I put this code in the custom CSS for the block where the label is located, custom CSS for the container that block is in, on the page, in the CSS stylesheet for the theme, and in the custom CSS for the website as a whole. Let me know if you'd like to help or ask more qualifying questions.