I'm looking for backgrounds with a specific art style (e.g., manga, retro). Where can I find those?

DeviantArt is a great resource for specific art styles. Search using keywords like 'manga background free,' 'retro comic background,' or 'vintage comic background.' Also, explore art communities on platforms like Tumblr and ArtStation, filtering by 'free to use' or 'creative commons' licenses. Be diligent about checking the license terms.