Custom Loading Screen Image

My friend asked me to make a custom loading screen for his server, but he never gave me an exact size to make it. Is there a proper size I should make this image so that it will fit everyone’s resolution, or should I just say screw it and make it whatever my resolution is and let the game re-size it by itself?

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You can use html/css to resize the image based on the persons resolution, so just make it a reasonable size so it doesn’t pixelate when it’s larger and so it’s readable when it’s smaller. If you need help with it, add my steam, I can happily host it for you as well.