Change colour of article description background from pink

I want to change the colour of the article background to white on the News Wall. How can I do this please, as I cannot find it in the css?
I'd also like to change the Tab colours for the categories and Load More. If I change this in the style.css will it be overridden if the tool is updated? Do I need a custom.css to ensure this?
Thanks in advance
Sue

Thank you for this tip for custom.css.
Can you point me to where the code is for the background colour of the article title, please? That pink colour?