Yarn build vs yarn build:production? What is the difference? I am still having issues understanding

Ok that makes sense now. Thanks for your help. I am having issues running build production though. It gives me this error “PostCSS plugin. Your current PostCSS version is 6.0.23, but uncss uses 7.0” . I just tried running yarn upgrade then ran just yarn then “yarn build:production” but it gives me this error now.