You may face an issue where you created a carousel and the white buttons are blending with background images of the same color, meaning the light grey background for these buttons is missing.
This is not an expected functionality, all three elements (title, subtitle, and buttons) should have the same light grey background as seen in the picture below, you could have changed that by mistake. Please ensure you haven't embedded any custom CSS that changes this feature.
To solve this issue, delete the carousel and recreate it again. For more information review the article Adding Slideshows on Site Pages Using the Carousel Modules.