Bootstrap 4 Full CSS over CDN is 23k minified & gzipped. There are Sass GUIs for novices, but you're correct I was referring to professionals. I don't understand the appeal of not using a build script, and, say going back to adding browser prefixes manually one-by-one? There's no benefit other than the hour you save at the beginning of your 3-month-long project editing your gulpfile.